I don't think distance is a factor per se, given how we played Chiefs at BG6. However I think the ultimate decision is down to PRL with some "input" from us. A number of seasons ago, all the games were arranged such that rounds 12 to 22 were the reverse fixture of rounds 1 to 11, meaning we ended up playing LI (I believe) as we'd played them at the LDH that year.
It' in PRL's interest to give us an opposition that can draw a croud, as this (along with Sarries large-ish game & Bath's clash) are three of the games that end up getting shown on FTA on Chanel 5, so making a big spectacle is in their interests too.
Personally I think it might be time to have the Tiggers as the opposition, seeing how the only time they've appeared at BG was the original one. Bristol would be a reasonable shout. Not sure about having the NotNots again, seeing how we've already hosted them twice (see also Gloucester, Wasps, & Saints). Sarries I'd prefer not to, & I think PRL would agree as it would make two of their showcase games on FTA involving the same two teams. Sale I doubt would be able to draw enough fans, and the same applies for Worcester.