Agreed - I think whilst only 21,700 at present the "South Glos bowl" can easily be extended to 26,000 and then up to 35,000 if needed. We will get to about 27,000 after much inconvenience and then won't be able to expand further without major works/buying adjacent land.
However, at least we won't be renting our ground from a uni and will share upkeep of ours with the rugby club.