I am a little bit lost... as an owner of > 250,000 GRFT, I have the needed amount to host a Tier 4 supernode when they will be ready (in June) but is it possible to already apply for this?
Until they actually get a lot of stores making use of GRAFT, supernodes will not be making much. I would guessing meaningful profit from supernodes is 9-12 months away.
Indeed, it's more to help them to test their supernodes of different tiers that I am interested to apply

I also need to check if the GRFT are not blocked during a long period in "stake" mode or similar constraint...
Ah cool.
Nice amount you got there, was it during the recent lows you got it or during ICO?
I was tempted to pick some up when it was around 200 sats, but got put off by the way things kept going wrong with their block chain.