I have also been looking into this. Normally I have just let GMs stream from the minors with no restrictions (besides max games played for eligibility).
Biggest problem is not the ability to stream prospects or usually block and hits specialists. This usually being AHL call ups that are trying to crack the roster on a 4th line or as a 5 or 6 D.
The problem is that this only usually benefits a small group of GMs that are extremely active and know how to exploit the league rules or the limits of Fantrax. And hey .... you can’t blame them.... But the biggest streaming GMs usually come out on top.
A minor league call up limit per week is probably the best suggestion. This could accommodate a majority of league set ups.
Anyone with other ideas?
I guess the only other other option is to lower your games played eligibility for prospects.... I usually allow 120 games played as the max for prospects to be eligible for the farm. Giving lots a time for development before they are forced to be on a GMs active roster. The drawback is that it also allows a GM to keep designated streamers on the farm longer as well.
So maybe lower the max games played for skaters to say 60 or 80 and allow GMs to keep them on the farm as long as you see fit. So they play up to 80 games going up and down and then the GM is forced to call them up full time or keep them buried on the farm after that.
Anyways... just spitballing.....
Regardless I will back you up on this as I think this is a common issue with Fantrax Commisioners