Well basically my idea for the endign would've been that a portion of krogan,salarian alliance etc soldiers made it hrough the portal and fought against the reapers on the citadel. On your way to find the trigger mechanism for the crucible you could choose to help Wrex and Grunt with their krogan teams. And depending on what choices you made they die or survive, but you'll also be able to help other teams wich will bring you a better or worse ending.
But in the end you dont find that little kid "the crucible" with the three bullshit options, you see your team mates fight alongside the soldiers you brought with you on this epic journey fight as one. And shepard runs towards a control panel depending on if you're renegade he'll get shot but manage to get up but he'll die afterwards, but in the good ending Shepard runs towards the panels shoots a couple of reaper soldiers slides over the floor and spins around and takes out a group of reapers. Then run up to the control panel and if you're renegade or paragon and what choices you made there would be alot of different endings, but the two main ones i want are these:
Paragon: A happy ending where Shepard survives and the mass relays are intact and you see everything that you did in the game and you see everything you worked for has come to a good ending and the reapers are destroyed by the crucible. (I'll add more details and opinions after i have seen everyone's comments)
Stupid idea: This would've been fun to see that Garrus and Shepard sitting at a beach near a destroyed reaper and have a little chat, and Shepards romance option is there too and the rest of the team (Including the ones who survived from ME2)- in my opinion...best ending ever...
Renegade: Shepard does not help the teams wich would've helped you reach the firing mechanism for the crucible so the result is that he gets shot multiple times as he makes his way to the crucibles firing mechanism. And that results in shepards death the Reapers are destroyed but the mass relays are also destroyed leaving the armada stranded.
(I'll add more after everyone's comments and opionions)