Frankly, it should not cost more than the 70-200/2.8L IS II (which is, indeed, substantially more than the current 100-400L). Hopefully, street price will drop under $2,000 in a year or so like it did with the new 70-200 (when I bought mine).
I hope the new one is solid on the 7D II and with a 1.4x TC. That would be the ultimate in easily hand-holdable reach.
I'll keep a possible Tamron 150-600 purchase on hold until we find out.