Psionics will always be a niche product Erik because it isn't traditionally associated with "classic" swords and sorcery fantasy.
I think that if you make it mechanically balanced, easy to track/integrate/prepare for, and include some really good fluff, you'll have a winner. I'd update the XPH as much as possible. After using that book I liked it and felt it was relatively well balanced, in addition, you won't be reinventing the wheel and will reduce development time for the product.
I might suggest mining some anime to get anime fans onboard, but that can be a double edged sword as some of the community has derision for the over the top treatment of magic/power that anime has and would automatically fear its inclusion in their game.