Habs are keeping Matheson this year to shield and support younger Ds like Hutson. Ideally, he is not a 25+minute-munching 1st pairing D, but, in a pinch, to help develop a younger D or two, using him in such a role again next year is not a concern.
Guhle's defensive stats improved in a 1st pairing role, even on his offside, and playing on the 1st pairing again as the RHD, unlike what some divas on this site claim, won't cripple his development.
The idea, here, is not to cater to Matheson, but to younger Ds' development by letting Matheson take on the difficult assignments for another year in Montreal.
Ideally, Hughes signs an actual top-4 RHD in the form of a veteran to play with Hutson, but I suspect Savard will hang on until the trade deadline to play the mentor role to Hutson (not my first choice).
I'd let Mailloux startle year in a 3rd pairing role with Xhekaj so as not to overexpose him defensively, early on.
Xhekaj was the only D to have positive defensive numbers for the Habs last season and he helped other players' defensive stats improve when they played with him (Savard, for example).
There was a brief chemistry demonstrated when Xhekaj played with Mailloux in Laval, so the reunion ought to prove worthwhile at the NHL level.
Next season, at least until the trade deadline, I expect to see:
Matheson- Guhle
Hutson - Savard
Xhekaj -Mailloux