I love gadgets more than most but doing an instrument rating with such avionics is a complete waste of time unless you are going to fly something pretty well identical (avionics-wise) yourself afterwards.
Especially as the way one uses an "advanced" GPS for SIDs/STARs/IAPs is very unit dependent, with more gotchas waiting to catch you out than most private pilots are going to discover in a year.
I had an option to do my IR in a Cesspit with a G1000 but turned it down. It would have taken an extra week to learn the avionics, which would be fun but very different to my KLN94/KMD550. And vastly more different than the spamcan most IMCR pilots are able to get their hands on.
The entry level for advanced avionics is around £200,000 and if that's your flying budget, that's great
(it's true for some people)
The other thing is that when doing the IMCR skills test, the examiner will just stick a piece of paper over it. It's not in the syllabus. With the JAA IR you might get lucky and be allowed to use it briefly but that's it. The syllabus in this area is still mostly in the 1960s.