Of course they're still relevant, the later firmware allows you to run a flex sensor directly into it and with the expansion harness you're able to do a bit more without the need of installing an I/O expansion box.
A few limitations of the Platinum are lack of support DBW, inability to run any style of trigger/crank/cam kit, no rolling anti-lag, no traction control, strain gauge input for sequential or dog boxes etc.
I would still use it, but brand new the price point between that and the Elite, one would jump onto the Elite.