I'm not a big fan of this idea. As much as it's unlikely that a 4th gets used for comp, it does happen from time to time, and I haven't heard about a clear penalty if someone does sign 3 comp players after trading their 4th. I don't think people would do this on purpose, but I can imagine someone putting in a bunch of bids, getting busy and ghosting for a day or two, and ending up with more players than they intended for.
You also have the situation where if someone changes teams or switches, you've limited the bidding options in free agency for a new GM (they are down to max 2 comp signings instead of 3 if the 4th is already gone).
I recognize that these aren't huge things, but I also don't think we're gaining a ton by doing this either, so the potential for either of these two problems is enough for me to lean against it.
You also have the situation where if someone changes teams or switches, you've limited the bidding options in free agency for a new GM (they are down to max 2 comp signings instead of 3 if the 4th is already gone).
I recognize that these aren't huge things, but I also don't think we're gaining a ton by doing this either, so the potential for either of these two problems is enough for me to lean against it.
GM 2050 - 2070, 2122 - presentPadres co-GM: 2117 - 2121
Cubs co-GM: 2098 - 2101, 2110 - 2116
Royals GM 2085, 2101 - 2110
White Sox GM 2089 - 2091
Expos GM 2071 - 2084
Orioles co-GM 2012 - 2014, GM 2039 - 2050
5 Pennants (2040, 2048, 2051, 2074, 2082)
4 World Championships (2040, 2048, 2051, 2082)