Hard to guess, it will depend of a lot off factors. My guess is, with the rule that EVERYONE forgot "T1 team are allowed to have a 2nd team in T1 if they are 3 GC player in it", I can see that happen in 2030 if one T1 team try this,
If team never try the "mix rule", then we will have to wait a 5 female roster and... Yeah maybe 2033 ?
Another factor that would speed up the process is that if tomorrow Riot says "Any GC team that qual to split 3 T2 is automatically qualified in GCC", that would solve the issue that GC team tryhard more their domestic league than the T2, and may make GC team a little bit better in T2
Gap is big, it's normal it's a long process. We need to be patient