[Brightcolours]

The Canon 100D is more like the Pentax Kr in features, and therefore closer in size:

http://camerasize.com/compare/#210,448

 

Or you can compare to the K-01, which is smaller but a bit heavier:

http://camerasize.com/compare/#285,448

That is one awful silly camera. None of the benefits of a DSLR (OVF, PD AF, ergonomics) and none of the perks of mirrorless cameras.

Or you can compare the K-3 to an appropriate analog in the larger, heavier Canon 70D:

http://camerasize.com/compare/#485,469

Yes. And would you recommend this to someone who is looking for a light replacement to a D610/600?

I also disagree with your statement that 'only a few [lenses] are of interest'. You forgot to add "to me" to the end.

 

As for performance/interest, I'll quote the PZ reviews:

 

15mm f/4: "The SMC-DA 15mm f/4 AL ED Limited is a another desirable pancake lens by Pentax. The lens is capable of producing very sharp and contrasty images at medium aperture settings."

 

21mm f/3.2: "The Pentax SMC-DA 21mm f/3.2 AL Limited is a very good lens but it is not as special as its longer cousins (specifically the Pentax FA 31mm f/1.8 Limited) nor is this really possible because of the increasing design problems when pushing things towards wide and ultra-wide angles."

 

40mm f/2.8: "The Pentax SMC DA 40mm f/2.8 exhibits a quite harmonious optical performance combined with excellent build quality."

It has so-so bokeh. The Canon 40mm is a nicer lens.

70mm f/2.4: "The Pentax SMC DA 70mm f/2.4 Limited is an great lens with no significant technical weakness."

It is a small aperture lens, not really of interest. The 77mm f1.8 is altogether a more interesting lens. I did mention overlap in the range.

If I were an APS-C shooter interested in compact/light lenses, those four Pentax pancakes to me have no peer for any other brand. Throw in the Pentax 17-70 f/4, according to PZ: "All-in-all a very harmonious package selling for a very fair price of around 480€/US$."

I did point out the peers. The Pentax 17-70mm has a better peer in the Sigma 17-70mm Art. And the Sigma 17-50mm f2.8 OS is altogether a more interesting lens too.

 

I do not feel the OP is best served with the dying Pentax lineup as "light" replacement for his heavy Nikkor 24-70mm f2.8 + D6X0.