A key should be introduced which gives you the ability to cook a grenade before throwing it (possibly a simple tap of that key). This allows in adversarial or coop that the target does not have the chance to move from the grenade.
You should also be able to adjust the power of the grenade by possibly holding your grenade throw key down or possible having a ranging system on grenades i.e. like launchers saying throw 5m, etc. Dslyecxi created a very good grenade concept which involved many abilities like this in the ARMA 2 engine like cooking, power, catching and re-throwing grenades, etc.
It would greatly improve grenades by increasing the overall effectiveness of them and also make them more deadly and enjoyable things to use. I mean who wouldn't like to play hot potato with another player!