Now as we know LF has plans for Sansa...he might actually want to marry her to HtH, (at least long enough for her to bear a child ostensibly by Harry before he meets an unfortunate accident and she becomes a widow,) or he might be planning on marrying her himself right off, or there could be some other party altogether, (perhaps fAegon but I consider that highly unlikely) but in any event, Sansa/Alayne's value to him to conditional on her being free to wed again.
He said initially, he was planning on marrying Sansa off when she became a widow...but as LF admitted, things are happening much faster than he predicted and he might have to act soon. Tyrion isn't dying so easily, (I don't think he'll survive the series, but he'll survive until ADOS, I'm sure,) which would appear to present an insurmountable obstacle....or would it?
Tyrion's marriage with Sansa was never consummated-that alone means it can be set aside by either the High Septon or a Council of the Faith. I could see LF pulling strings and making bribes to the right people to see to it that such a ruling of annulment is made by the Faith quietly but not announced right away to alert the Lannister's, with LF planning to make the documents public only at her wedding to ensure the legality.
(It's also possible since LF knew all about Tyrion's first marriage, he might be planning to use that to get the marriage to Sansa declared invalid on the grounds that Tyrion was never free to re-marry-but I think the non-consummation angle is probably simpler.)
Alternatively, I sometimes wonder if Varys might have reasons of his own to dissolve the Tyrion/Sansa match if he wanted Sansa free to re-marry-either to fAegon or some other important ally like Willas Tyrell as being the way to finally secure the Tyrell's for fAegon's side or some such deal. (We know he sent Sir Shadrach after her for some reason.)
Regardless, of who gets the marriage annulled, or how, or why, I think Sansa once realizing she's free of that mockery of a marriage she had with Tyrion, will be less than eager to wed again-and will probably use her newfound freedom to 'fly away' bird style and make way to the North...possibly in the company of the Blackfish, or Brienne, or even Jaime Lannister.
If she ends up meeting with Jaime Lannister, then that might mean a meeting with Hoster Blackwood-and it occurs to me that a Sansa/Hoster match might be in the making with them becoming the future Lord and Lady of Riverrun and the Riverlands.
There are several reasons I think GRRM may be setting this up;
1. Sansa is consistently referred to as the "little bird." She is surrounded by bird imagery. Hoster is from Raventree Hall.
2. The Blackwoods of Raventree Hall are indeed one of the oldest and most powerful families in the Riverlands-they go back to the first Men, and were rumored to have been Kings of the Riverlands just as the Starks were once Kings in the North. They're one family, outside of the Lord Paramount Houses, (and let's be honest here-most of those Houses are on the wrong side, or have burned bridges with the Starks,) that can honestly claim to be 'good' enough for a Northern princess.
3. Hoster's name is freaking...Hoster. Like that of Hoster Tully the last truly great Paramount Lord of the Riverlands. He would be acceptable to the Riverlords, as no Frey ever would have been even before the RW.
4. The Blackwoods are one of the few families south of the Neck to still worship the Old Gods-and they have a Weirwood tree. This makes them a good match for Sansa who keeps the New Gods and Old Gods close to her heart. It also suggests that culturally, the Blackwoods are a mix of the SOuth and the North...just like Sansa.
5. Tytos Blackwood was one of Robb and the Tully's most loyal supporters-even Jaime was impressed by his honorable behavior. Which means he's the sort of guy, Sansa would like as a father-in-law. And it would be nice if at the end of this series some people who actually behaved honorably got rewarded for a change.
6. Most importantly, Hoster might be a good match for Sansa. He's age appropriate, and obviously a very thoughtful, intelligent young man, who seems like a good guy. He might be gangly, but he's hardly ugly, and she might like him if she got a chance to know him. (It's sort of the beauty with the book worm thing.) I also enjoyed hearing his speech about the pointlessness of the Bracken/Blackwood feud-it suggests to me that Hoster is the kind of guy who's more interested in re-building and peacekeeping than petty feuds-which will certainly be what we need running estates when all this is over. Plus since Hoster is a younger son and not the heir, it won't create the awkward situation of inheriting two estates to rule over, and instead Tytos will get the satisfaction of two of his four remaining sons being very nicely settled as lords...and now having the kind of family connections to help all their remaining siblings do quite well too.