I'm doing my ME on a Seneca and IR on a Twinstar. Best of both worlds. I learn to fly twins in the heavier, more dated Seneca, and then choose the easier route through the IR with the Twinstar. It's simple economics: FTOs want to compete on pass rate league tables to get more students, so more and more are choosing the Twinstar for IR training because it gets better results.
Moreover, from a personal point of view, in common with most wannabes, my aim is to get my fATPL as soon as possible so I can get a job flying for a living. I'll probably end up flying modern EFIS/FADEC equipped turboprops or jets and I can't really see how doing an IR in a Twinstar can be bad preparation for that?
But let's face it, the actual amount of twin flying you'll do before getting that first job is going to be so minimal that the choice of which aircraft you use for the IR is going to be less important than your basic flying skills and you can hone those better on a taildragger. IR in a Tiger Moth anyone?