I have several objections to an X4 with all (or nearly all) the original cast:
1) it could easily look like a retread just for the sake of making money;
2) having killed or depowered many of the characters in X3, it would be hard to bring them back without it being absurd;
3) too much of the budget would be spent on paying an expensive cast;
4) even more of a scheduling nightmare.
They either need to go off at a tangent with just a few members of the original cast, or wait a few years and go for a reboot with a cast of unknowns.
1) it could easily look like a retread just for the sake of making money;
2) having killed or depowered many of the characters in X3, it would be hard to bring them back without it being absurd;
3) too much of the budget would be spent on paying an expensive cast;
4) even more of a scheduling nightmare.
They either need to go off at a tangent with just a few members of the original cast, or wait a few years and go for a reboot with a cast of unknowns.