I don't mind Rebecca joining, though what I would prefer (at this point) is that no one joined ... EVER, just stick to 9, though I know Oda would make a new member work
but I can't pretend that I still after 10 years kinda divide teh SHs on the core members that joined pre GL and the other 4 even if all of them are on my all time fav character list, I think that another divide would be made if a member joined post TS
though I have to admit that 1 of the reasons I would love 9 members is also the fact that it is the same number as the number of the members of the fellowship so my two fav stories ever would have the same number of main characters
the ones I would like to join the most probably (and by that I think 99.99% sure) won't join (other than Jinbe), but still my preferable choice would be 9 till the end