Totally agree. The trend seems to be to push towards FX (makes sense considering the lack of support for DX lens-wise other than kit zooms); so they should condense D3xxx and D5xxx into one body, and then leave the D500 as the pro body for those that need the crop. I'd also kill the D6xx series, and just have D7xx and D8xx in addition to two Dx series flagships: one super high res/low fps for commercial/studio photographers and one low res/high fps (basically the D5 as is). Kill the DF as well and make a proper mirrorless body similar to what Canon did and that'll give them 3 price points for dslr's, no overlap, and ideally all needs met.
In a perfect world:
D3xxx/5xxx hybrid: 24mp, working snapbridge or a better way of sharing photos...maybe directly to FB and IG, basic 4k video implementation, 120fps 720 for a gimmick, tilty-flippy touchscreen. ~$750
D500: leave as is, the high fps, best AF body for sports/wildlife ~$1800
The tricky part is there's room for the D7xxx series to exist in between the two, so they could theoretically keep it if they can make it worth $1250.
D6xx/7xx hybrid: 24mp or even 30mp, 8fps, same AF as D750, working snapbridge, tilty-flippy touchscreen, 4k and all the fancy video features (10bit 4:2:2 at high bitrate/flat profiles/peaking/zebras/etc) you'd find in a GH4/5 for example. Targeting video centric people who are leaking to Canon/Sony/Panasonic ~$2200
D8xx: 54mp, 4fps, D5 AF system, touchscreen ~$3400
*With the exception of the 3xxx/5xxx body, the other 3 should be more consistent in their build quality. Maybe D500 style for all, with varying levels of mag/alloy as you move up the ladder. Consistency body-wise has been a big issue for Nikon.
D5: keep it and it's update the same, low res, rugged, super high fps body ~$5000-5500
D5x: same as D5 but with 70-80mp, give it the tweaked 51pt AF, 16bit color, and low fps. Target commercial shooters who are renting MF or those looking at the new Fuji, price at ~$7500-8000
Mirrorless options to rival the M5/M6, an entry level and upper level, both ~24mp DX, one with EVF, one w/o. Give them touchscreens, decent video, and electronic shutters with decently fast fps. Must have working snapbridge (ideally something better). Pretty much follow what Canon did, but with one big caveat: make it take f-mount lenses. No adapter if possible. Size the lower level around an A6000, and the upper level around an A7.
And last but not least, follow that up with some smaller f2 DX primes (which benefits those that still use the D3xxx/5xxx, D500, and the new mirrorless options. 14mm, 18mm, a 2.8 pancake 28 or 30mm, update the 35mm, and then add an updated wide/standard f2.8 lens like the old 17-55mm.
IF they could do all that, they'll consolidate the lines a bit and differentiate them a bit more. Working mirrorless, that has access to all of the F-Mount stuff would essentially kill every other mirrorless option if they don't screw up the body itself. Adding some new primes that are smaller and target DX and the mirrorless users also shows that Nikon intends to support the format (DX) and the new mirrorless (because no one knows what's going on with the 1 series)