2025's not that distant; President Trump could be taking a victory lap then. And the Glazers are pretty heavily invested in both teams; one of Malcolms sons sits on the board of each, with two more sitting on both teams boards. Perhaps most importantly, Man U and the Bucs are both reliably huge cash cows, so why would they give up either?
Of course, Tampas profitability is almost purely a function of NFL revenue-sharing, so that's an argument against moving, since they aren't good enough to maintain that revenue stream on their own, especially in a foreign market. However, if the other owners bite the bullet and accept that any foreign expansion will require heavy investment with negative return for several years, moving two teams yet maintaining their share of NFL revenue could be the answer.
The real question remains how to establish and maintain enough teams to constitute a full scale European LEAGUE. There's a strong argument to start with the UK, exploit regional rivalries and expand to the Continent later, but I'm unconvinced Britain has enough large markets to sustain that. That's the biggest argument for London and Manchester: After them and Birmingham there aren't many cities big enough to support an NFL franchise.