Assuming there will be more companions in the final game to have a four companions party seems not so great. The advantage of D&D and Pathfinder rule set in video games is (imo) to have a lot more classes then in other games (like Dragon Age etc). So it would be nice to have a six-companion-party.
I also don't like the fact that we don't have to possibility to group our companions. Very often the selected leader of the party runs into some foes, the battel starts and the other companions are far behind. At least they should stick togeather like glue.
To my knowledge in all versions of BG you couldn't take all the companions that were available with you. You were always forced to leave companions behind.
In the original BG, when companions just stood in the spot that you left them, if you had a full party in the mines and wanted to pick up another character you had a to leave a character in the mines knowing they would be drowned. That felt bad.
There is always a limit placed on the number of companions you can have.
A party of 4 is perfect for me. (Especially in a turn based game)
Your mileage may vary.