HallowETF2L has like 300 teams a season while ESEA-NA has barely 100 afaik. ESEA can't expect all 300 EU teams to switch, because of that difference in mentality and financial situation. But having 100 teams playing in ESEA-EU within a year seems reasonable to me.
First season of TF2 Open they had 20 teams. Currently 1 day after this is announced there is 16 teams pending. The 2nd season of TF2 they had 30 open teams and 8 invite. I think that those are pretty reasonable goals for EU.