Ya I get your point but it's a slippery slope to a whole can of worms...
Seems logical enough to let an O35 player freelance among lower division teams in other leagues, but where do you draw the line? Some O35s are very good players and often CAT into Open, so I guess the extreme example would be all of EDC's O35 Prem decides to go off to the Valley one weekend and play with some guy on the team's nephew and his buddies in Div. 2 FVSL and maybe it helps them get promotion, or win a cup game or keep another team out of Provincials etc.
The point is the lines get blurred real quick. They need to be registered in whatever league they are playing in for insurance purposes in case they break their leg and don't have medical. Plus what happens if the guy from VMSL masters helping out in the BMSL open gets sent off?? Is he suspended in both leagues?? Does he just vanish into the wind? What happens if it turns into a "Milad-style" incident? It sounds far fetched, I know, but what is to stop teams from just hiring goons from masters to come in and injure opposing players and then vanish of into their own league?
Then what division is "low enough" for them to play in? Can you play masters in the FVSL and then open in the VMSL? Who manages this coming and going of players? Can you play in cups? Provincials? Can you play on multiple teams in the same league if your Masters in another league? Ie can @machel from VMSL Masters play one week with Team A in FVSL Div. 2 and then the next with Team B in FVSL Div. 2? Who keeps track of that? Or can you play on one team in each Division?? It gets real confusing real quick.
I think at the end of the day it's just about trying to keep the playing field and level of competition as even as possible for everybody. Want to play with your friends for fun? Play UrbanRec.