If Wales walked away from the ECB structure it could field a T20 side almost immediately. It would be relatively successful because all the players in it currently have come through the ECB pathway, and into a minor county, or county structure.
However i dont believe it is in the interest of cricket in Wales to walk away from this structure. In the same way that i dont believe that Cardiff, Swansea, Newport, Wrexham should walk away from the English league structure. As being in both is more beneficial to them than not.
Ultimately there is not much support from the public in Wales towards cricket. Glamorgan are one of the poorest supported county sides.