It'll only work
if they stand on one leg, blindfolded
Famous Pentagon boffinry powerhouse DARPA has made a new announcement on its "One Shot" programme, which ensures that a million-to-one shot will – as on Terry Pratchett's Discworld* – hit the target nine (well, six) times out of 10. Boatswain's Mate 3rd Class Todd Hubert - and his spotter, Seaman Chad Luck - of the US Navy …
the primary purpose of the 2 man team is psychological.
a) you get to split the responsibility – he told me to shoot/I only said to shoot I didn’t pull the trigger
b) you don’t want to let you mate down
c) you don’t want to be shown up
d) the sniper knows no-one is sneaking up on him while he's on-scope so is less twitchy
which all means the sniper is more likely to pull the trigger on the target and less likely to go home and do the same to themselves.
So I can see how it would make sense in terms of increased lethality but I don't think it makes for smaller sniper teams.
rather than the 2nd man being primarily a spotter for the sniper, use of the clip-on version would allow him to be more 'situational awareness' and 'mission management' or whatever the relevant buzz-phrase is. At present there will be significant periods when both men are staring down very narrow field of view scopes which creates risk. Letting the sniper get himself all setup on his own with the spotter using regular binox or similar for general scanning gives the best of all worlds. He can still do target confirms and shoot orders etc for shared responsibility.
More likely would be a laser-seeking round for the XM-25. The rounds the gun fires are 25mm in diameter, which would seem to be plenty to build in a miniature seeker head and maybe leave enough room for a small explosive charge. The built in ballistic computer in the XM-25 scope would get the shot as close to a direct hit, a simple laser preojector unit would provide the guidance spot, leaving the bullet the minimal amount of terminal manouvering to get that first round hit.