OK, for all those who might be interested here is what's in that WTP90 iron.
The heating cartridge has 4-pin connector. Looking at the plug (towards the tip) with a slot in that plug at the top, pins numbered CCW with pin 1 is top left, pinout is:
1 -- Common Heater/PTC sensor
2 -- Heater (~6 Ohm, 90W @ 24V)
3 -- PTC sensor (probably Pt100, crappy multimeter shows 110 Ohm at room temperature)
4 -- Tip (for grounding)
Now the handle part, looking into the plug from pins side with key at the top, counting CCW, pin 1 at the left top, pin 6 (right by the key) missing, center pin is pin 7:
1 -- Cartridge pin 1 (Common Heater/PTC)
2 -- Cartridge pin 2 (Heater)
4 -- Cartridge pin 3 (PTC)
5 -- Cartridge pin 4 (Tip, for grounding)
The interesting stuff is between pin 3 and pin 7, not connected to anything in the cartridge, handle only. It is 2 kOhm resistor (seems to be Weller's ID for 90..100W or so) when handle is stationary. When handle moves this connection breaks momentarily so pin 3-7 connection becomes open. I assume it is some pure mechanical stuff that breaks contact when moved (mercury switch or whatever.)
That should be sufficient to make a DIY power station or hack any existing one to work with WTP90.
There is absolutely no reason for buying those WT1/2 stations -- they do not provide anything special and all of those (except WT2M) are 24V-only so they won't work with 12V Microtools (WRMP, WRMT etc.)
And as it's already been said WTP90 is the ONLY member of WTx tools -- they dropped everything else in favor of WXx stuff to rip off their customers one more time as it is not compatible with any older tools.