Welcome to the postal vote for same-sex marriage.

Dutton first floated a postal plebiscite in March, arguing it was the "sensible approach" because the Senate had blocked the government's preferred plan to hold a compulsory vote on the issue. The postal idea, which is supported by Queensland's Liberal National Party, is based on the understanding that if the vote was voluntary, the government would not need Parliament's approval to go ahead.

Now with the very real prospect of pro-marriage equality Liberal MPs crossing the floor to bring on a vote on same-sex marriage and a showdown party room meeting set for next Monday, the postal vote is looking more like a live option as a way to keep the peace.

But is it a viable compromise? Or will it end up creating more problems than it solves?

Australia is used to voting in person at a polling booth. But the Australian Electoral Commission has plenty of experience conducting postal votes. On top of optional postal voting for people overseas or in remote areas during regular elections, the AEC arranged a postal vote for Queenslanders on council amalgamations in 2007.

However, the last time the AEC organised a postal vote at a national level was in 1997 to elect delegates for the constitutional convention on the republic. A recent paper prepared by the parliamentary library estimates that in today's dollars this cost around $40 million (compared to the estimated $160 million needed to conduct a compulsory plebiscite). The bulk of the funds went on the production and postage of voting papers, advertising, divisional office costs and public information.

It wasn't a speedy process. The non-compulsory vote took more than three months from the time prime minister John Howard announced the election dates to the declaration of the results. This included two weeks for the ballot papers to be mailed and about a month for people to send them back to the AEC. It's arguable a postal vote for same-sex marriage would not need as long – as it is asking a more simple question and does not need a nomination period for delegates.

Surprisingly (if you look at the way he avoided answering questions on it this week), Prime Minister Malcolm Turnbull was mightily opposed to the postal approach in 1997, as leader of the republic's "yes" campaign. In an opinion piece for The Australian, he said postal voting "flies in the face of Australian democratic values".

According to the article, unearthed by Crikey, Turnbull raised concerns about the high number of people who change their address between elections. "These voters will not get their ballot papers. Not unless they ring up and make a special request, and who will get around to doing that?"

Turnbull also said young people and Indigenous people in remote communities were at greater risk of being disenfranchised because they tend to move more often. Young people were certainly less likely to vote in the 1997 ballot than any other age group. As a percentage of those enrolled in their age group, only 34 per cent of 18-25 year-olds participated in the postal vote. This compares to 50 per cent of 46-55 year-olds and 59 per cent of those over 56.

It's also true that young people are less involved in elections, generally. In the 2016 election, 95 per cent of eligible voters participated, compared to 86.7 per cent of eligible 18-24 year-olds. There are fears among same-sex marriage advocates that given support for marriage equality is more pronounced among younger people, a postal vote will harm the "yes" camp's chances if there was a vote.

Monash University senior lecturer in Australian politics Nick Economou isn't convinced by this argument. He notes that because same-sex marriage is an issue that young people care about, they are more likely to want to vote. And even though they do live in a digital world, they are also more than capable of using a pen and an envelope (it's not that hard).

"I have full confidence young people would be engaged," Dr Economou says.

In his 1997 tirade against postal voting, Turnbull also warned that a postal ballot lacked secrecy and integrity. "In the voting booth each of us votes alone. Without the pressure of husband or wife, parent or child. When the postal ballot arrives in the letter box how many people will be compelled to vote one way or other by a strong­-willed friend or family member?"

Economou similarly notes there are no real protections against one person in a household simply filling out papers for others they live with, perhaps with the more benign intention of helping rather than bullying.

Another significant question mark hovering over the postal vote is its ability to deliver decisive victory or closure. Non-compulsory voting means less people – of any age group – will vote. In 1997, just 47 per cent of voters sent their ballot papers back.

As Sydney Liberal MP and same-sex marriage opponent Craig Kelly told Fairfax Media last month: "My concern would be that a voluntary postal vote may not have the authority of a compulsory vote at the ballot box. It would be very easy for one group to say they would boycott it and not recognise the result."

So, beyond its proponents within the Coalition, it is difficult to find fans of the postal vote.

Those who are against same-sex marriage, such as the Australian Christian Lobby, say the postal vote is an "option that should be canvassed" – given the plebiscite was blocked in the Senate (by Labor and the Greens). But the lobby's managing director Lyle Shelton adds his preferred option is for the government to "just show some resolve" and take its plebiscite policy to the next election.

The "yes" camp – who vociferously opposed the idea of a compulsory plebiscite – don't even want to entertain the idea of a voluntary one. Australians for Equality executive director Tiernan Brady says a postal vote sends a "terrible message" about LGBTI Australians.

"I don't think the dignity of one group of people should be subject to something that's written on the back of an envelope."

There is also talk of a legal challenge, even before the precise details of the proposal are made public. Marriage equality advocate Rodney Croome told The Australian he was seeking legal advice on the whether the non-compulsory vote would still need the authority of Parliament, given it would involve the spending of public funds.

Melbourne University constitutional expert Adrienne Stone says the government may have the capacity to spend money on the postal vote under the heading of "ordinary services of government". Professor Stone said it could potentially be argued the government was legitimately testing the opinion of the people as part of policy formulation.

But Stone, the director of the Centre for Comparative Constitutional Studies, said this is still a new area of law, in the wake of the High Court's 2014 school chaplains case that ruled government spending should be subject to parliamentary oversight.

"You can bet your bottom dollar there is going to be a challenge."