That and/or the specialists. So for example Brazil. Andrade has expressed an interest in the event in LA, but with the Euros rules about 1 WAG and 1 MAG only, she wouldn't be eligible due to sitting out floor (this is assuming arena constraints will stay what they are and the qualifying apparatus will remain the same). Whereas if the top Brazilian athletes qualify a team spot, Brazil could potentially compete Flavia on floor, Rebeca on vault and either on beam.
@MaryClare they haven't said afaik. At Euros it was any delegation with at least one MAG and one WAG competing the relevant events.
But my guess is they won't restrict it to full teams because that's potentially a very small pool and they'll only get 10 months notice of the size. There were 8 countries with 2 full teams in Paris. Which might work well, since 16 at Euros felt a bit unwieldy, but that means they're screwed if there only ends up being 7 next time. I can't be arsed working out how many countries had at least one MAG and one WAG in 2024, but it widens the pool considerably. Again it boosts the event if you can potentially have relatively big names from lopsided programmes like Ukraine MAG in there.