I wouldn't mind either of these, I own a P226, MK23, and AR15. And they already have the 227 which is essentially the same thing as a p226 just a .45. But the Mk23, I've not seen that in a game since metal gear solid and Rainbow six Vegas. I'd love that gun to make a return.
Personally I'd love to see these make it in at some point.
FNH F2000
FNH M16A3 (or A4)
FNH M240B
H&K XM8 (LMG, DMR, RIFLE, COMPACT VARIANTS)
H&K SL8
H&K 417
H&K HK433
H&K VP9
H&K P30L
SIG SAUER MCX
SIG SAUER 552 COMMANDO (SG552)
SIG SAUER M400 PREDATOR
SIG SAUER P320
MPS AA-12
CHEYTAC M200 INTERVENTION .408
BARRETT M98B
BARRETT M468 SPC
BARRETT M-82A1/M-107
KNIGHTS ARMAMENT COMPANY M110 SASS
LWRC SABR (SNIPER AND BATTLE RIFLE CONFIGURATIONS)
M1A SOCOM
BERETTA ARX-160
BERETTA MX4
BERETTA PX4
I LIKE to think of myself of fairly well versed in firearms. Bit feel free to correct me if you see any mistakes. I feel like the bigger the list perhaps they could pick and choose.

[/QUOHK TE]
HK SL8 was made for the civilian market and is just a G36 with a thumbhole stock to get past the 1994-2004 assault weapons ban so would be better to just have the option to have the standard G36/G36K maybe as longer barrel options for the G36c in game allready.
HK XM8 is just a G36 with different furniture/receivers so as to be able to sell it to the U.S. military without it looking like they were arming the U.S. with a German Service rifle. So we could get the XM8 as a reskin of the G36 have the same stats just make it look like an XM8.
Barrett M468 is known as the Rec-7 nowadays, would be great to see an AR15 in 6.8 SPC Rec-7 would be a great choice would be nice to see the shortest longest variations of the Rec-7 as an option in game
https://barrett.net/firearms/rec7/
I'd go with the Barrett "MRAD" over the "98B" it's the improved version of the 98 with more options for caliber conversions and I think it's a tad lighter.
and the M240L (with the collapsible stock) or Barrett 240 LW/LWS over the standard m240b as it's considerably heavier than the others mentioned.
All in all good list though. Not trying to be a smartass or anything just seemed like you might be interested in knowing more about some of the firearms you mentioned, and I also don't trust ubi to get anything with guns right so it's good to correct people as ubi might get feedback and implement things they shouldn't as a result.