I can see the potential benefits too. A League is lower quality than MLS, but still good level for developing players. Similar styles of play and even traveling requirements are same.
Problem is, A League has even more restrictions on foreign players and limited spots. Wellington would want players that can make immediate impact on first team. And they'd probably be limited to attacking players. And TFC won't like to give up players that can contribute to first team.
I'd like to see close coordination for TFC and Wellington to identify young players that needs game time, but can still contribute to Wellington. And very few TFC players fit that criteria IMO.