The advantage of having a FF is that the lenses targeted to FF can also be used on APS-C. Those lenses are available for use in two separate markets. But there is still IMHO a need for a good line of APS-C dedicated lenses. Pentax (arguably) has one of the better line ups of dedicated APS-C glass and I see no reason they would not continue and even strengthen that line. We already have 10-17, 12-24, 18-135, 16-85, *16-50 and *50-135. Plus the DA Limiteds. I think all of those (except the recent 18-135 & 16-85 and Limiteds) are in need of updates and if I remember correctly a replacement for the 12-24ish is on the lens map. If they re-do the *16-50 and *50-135 in a year or so and re-do the 12-24 I don't know what else would be needed in dedicated APS-C.
The rest of the primes: 20, 24, 28, 35, 50, 85, 135, 200, 300 would also be FF lenses. The 15-30, 24-70, 70-200, 150-450 would also be dual purpose lenses. There are also the FA Limiteds which many expect to be updated like the DA Limiteds were. Add at some point down the road a 300 f/2.8, a 400 f/4 and a 600 f/4 and you have a fairly good catalog of glass. Not everything, but surely enough to keep most people broke.
And then we can start to wish for more exotic things like 200mm macro and tilt/shift lenses.