I like the idea of the felinids and it would be kinda cool to see something like Eastern Beastmen with the Astra Militarum equipment. On the other hand, it would completely ruin the Imperium of Man setting of the 40k. They would end up just like the other abhumans - cheap and expendable cannon fodder.
I like the way you drew him - his anatomy and pose are pretty good. His clothes and flak armor are also very nice, but you could add some more details - like folds on his clothes or few dents here and there on his body armor.
The Skull insignia on his shoulder pad is spot on! Adding a regimental number under it could give it even more depth.
Choice of his gun is interesting - a prototype submachine gun is a perfect choice and it fits 40k standards pretty well :D Maybe you could try to modify it even more - add some more parts or imperial insignia for example.
You should draw more things like this because it's definitely your strong point. Maybe you should try and give this work a finishing touch - try with ink or something similar. I'm sure the results will be pretty damn solid !

Thank you very much for the comment. I really don't spend much time on the stuff I doodle, I tend to lose interest very quickly which is why they're always unfinished.
My interpretation on the 40k felinids is that they are genetic constructs, built for their enhanced senses and hunting instincts, with their loyalty leaning towards the Adeptus Mechanicus. That sort of sets them apart from beastmen and mutants that are created by random mutations from chaos or their environment.

I perfectly understand what you mean about leaving stuff unfinished and losing interest :D However, you should give it a try - it can only get better from here. You have many works in your gallery so it must have some kind of meaning to you if you're still doing it.