Powerful new dynamic could be brought to northern stage
Fianna Fail organising here would make nationalist politics in Northern Ireland exciting again.
But it's been talked about for so long without any practical developments that some wonder if it will ever happen.
"It's like trying to arrange a wedding," an SDLP insider says. "The SDLP is the groom making the proposal. It all hinges on the Fianna Fail bride saying yes."
The choreography of any such union would be carefully pre-planned, he says. An outright merger isn't on the cards.
Rather, the SDLP would leave the stage, allowing for Fianna Fail to enter as an all-Ireland party.
While key figures in the SDLP believe that only Fianna Fail is capable of posing a viable alternative to Sinn Fein here, the southern party's commitment to making such a leap is the big question.
There is much at stake for Fianna Fail if it goes wrong.
Sinn Fein could use a poor performance on this side of the border to clobber its rival in the Republic.
However the Fianna Fail leadership has been warned that leaving Sinn Fein as the only major political player organised on both sides of the border could ultimately hurt Fianna Fail on its home turf.
SDLP supporters of political realignment maintain that the policy differences between the two parties are minimal.
However, opponents say the union would be an unnatural fit.
Many in the SDLP, including its leader, are more left-wing on economic issues than Micheal Martin's party.
The strongest argument in favour of realignment is that it's impossible to see the SDLP ever being seriously competitive in northern nationalist politics again.
Next year's council elections will surely result in yet more losses. Neither Mr Eastwood's polished media performances nor the party's past glory days can stop it.
Sinn Fein no longer seriously fears the SDLP. Fianna Fail coming north would put the wind up Michelle O'Neill's party. But it would be vital for Fianna Fail to carve out its own image here and in particular to bring in new faces. If it's seen just as a regrouping of those whom the electorate have increasingly abandoned, the project will fail.
The SDLP will never be able to match Sinn Fein in terms of grassroots organisation or finances.
Fianna Fail would deliver resources to the table of which Mr Eastwood's party can only dream.
If handled and marketed right, the southern party's entrance onto the northern stage could bring a powerful new dynamic into play.
Much rides on whether Fianna Fail says 'I do'.