I’d love it if H&K came out with a USP in 10MM
A .22LR version of the M&P, and/or a .22LR conversion slide to use on existing M&P’s. Cheap training!
M&P with a Glock trigger. 
Without a doubt, the gun I would buy this minute is a p7m8 with a polymer or other lightweight frame.
They already make an HK45.
I have a few that are a in different directions.
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CZ SP-01 9mm with aluminum frame, front scallops(like standard models), quality nightsights, shortened contoured beavertail, full length dustcover under a full IDPA box length slide, and extended threaded barrel. This would of course have to be as reliable as sig,hk,M&P. And for gods sake give it a competition hammer to make the reset not so horrible.
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S&W M&P9 with thinned contoured beavertail making it not painfull to shoot with thumb safty. It would also need extended threaded barrel, 5in slide, and external hammer.
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Sig 226 9mm with full IDPA box length slide(approx 5.xx in), build in magwell similar to Heinie style weld on for 1911 only on alluminum frame, shortened overtravel, extended threaded barrel.
Carry gun would be same as any above with 4in slide and sig 229 length grip and no threaded barrel.
FWIW I find the CZ to be practically perfect as is just needs reliability and front scallops on slide. The shortened beavertail and longer slide just make it nicer for gun games. The S&W is also quite near perfect but needs the thumbsafty beavertail area worked to achieve what I feel it needs to be more ergo. The Sig is likewise near perfect but it would be nice to have a longer “gamer” slide available. The threaded barrels would be drop in extras because I like quiet guns:D.
If I was to build one from scratch it would be
-9mm
-rear decocker (ala HK)
-TDA
-Aluminum frame with one piece frame/dustcover tactical block that has steal threaded insert so you can mount a can on it without booster.
-4.5in barrel
-either fixed barrel or maby the rotating style that would allow the front of barrel to keep seal with tactical block/dustcover to make the suppressor not just a muzzle weight.
-slide lock(for single-shot suppressor use) probable in 1911 style safty position for leverage.
other variation
-same same as above but with 2in barrel and full length duscover designed to accept a 1.25 od fast attach can and have dustcover extend to end of can.
I always wondered why Glock never made a single stack 9 or 40 for a CC gun.
+1 to a line of single stack Glocks. Full size 9 or 10 shot single stack 10mm especially.
A striker fired FNP9
Oh good call. Didn’t even think of that one. 
-Single stack 9mm Glock/M&P
-M&P9 identical in size to a G19
+1 on a single stack M&P/Glock
Also, I think FN should introduced a modernized BHP.
I’ll second (or third, fourth, whatever we’re up to) a single stack 9mm Glock or M&P preferably in all the various sizes they’re in now…
Single Stack Glock as mentioned
Reintroduce the S&W revolvers without lock and MIM parts – I’d likely be bankrupt soon
A Glock in 7.62x25.
I would like to see a striker fired, polymer frame SIG-Sauer pistol in .40S&W available in a full-sized, mid-sized/compact, and sub-compact frame sizes with the more diminutive framed pistols capable of utilizing the magazines of the larger framed brothers and sisters in the family, because if there isn’t such a pistol like this soon I fear it will be the end of SIG as a serious supplier of pistols to law enforcement.
Ruger MkIII in 22 mag
A slim single stack 7 to 8 rounds small 9mm pistol that is not built wide enough to be a .40 SW
Double Strike Single Stack 9mm Compact/Sub Compact from GLOCK… Hold the finger grooves…
I would like to see S&W make an M&P 9mm/40S&W in a medium framed “compact” size identical to the size of the M&P .45 compact. This would be the competitive size to the glock 19. One of my biggest complaints about the M&P9/40c is that they cannot fit a full size light, and this would solve that issue.