I would have definitely wanted to see further relationship development between Alex and Joey and Gina and Jimmy. Perhaps a pregnancy for Gina, since she had the scare. I would want to see Joey working hard to learn the ups and downs of being in a one woman committed relationship, and also to go on to an even bigger and better project. Adam Goldberg would have joined the cast as a regular, and perhaps he and Michael could make some sort of scientific breakthrough together and consider marketing it. Michael would get into a serious relationship, maybe with he and Abby 'moving forward' as she wanted. Then he would get his heart broken, perhaps cheated on. He would go through a rough time, finally giving in to sleeping with Bobbie, only to meet someone even better and find an even greater love, and I'd have wanted her to be pretty because his kindness overrides his moderate geekness. Zach would still make occasional appearances, and with Joey's help finally get a great role, perhaps in Joey's next movie, and he begins to rise in fame as well. Howard would still be around from time to time with his wonderful kookiness, and he would maybe find a great girlfriend as well. As other minor plot twists to be used as filler, Donna (Kelly Preston) could return again after splitting with her husband for good, and Joey would have confusion about what to do. He would NOT cheat on Alex, realizing that his time with Donna had passed and he was in love with Alex, truly. Dean would have a heart attack, and Alex and Joey would both aid in his recovery because they still care about him regardless. As a Sweeps Week stunt, there would be an hour long episode surprise as Chandler visits, perhaps for another big movie premiere. Maybe Chandler could double take on Jimmy, saying maybe he knows him from somewhere, just to acknowledge that Goldberg played Eddie in Friends. As a season finale cliffhanger, Joey would propose to Alex, which would be a nice pause if it had been renewed, or her saying yes if it hadn't gone on for a fourth season.
Whew! How's that for imagination? I think I've thought too much about this. Heh. I'd love to hear more ideas from others. Or maybe someone wants to write some fan fiction? That's allowed on the forums too!