I could absolutely see us having both for a spell to be fair.
Although Gomez is a centre-back, I see him more as a utility player that can cover at centre-back, left-back or right-back in emergencies, which is very valuable when he is fit. Though we know about his bad luck with injuries.
No idea if Slot sees it that way, but if we think of it through that lens then I would look at our (potential) centre-back situation as follows -
Van Dijk
Konaté
Guehi
Leoni
(Gomez)
Bearing in mind that Van Dijk is 34 now and given the potential of a 60-game season (or approaching that) if we go quite deep in multiple comps, I think we could have both Guehi and Konaté. A time surely comes where we don't expect Van Dijk to start 38 League games AND all of our Champion's League games as well.
We've seen how "easy" it is to get out of the Champion's League League stage - you don't want to leave anything to chance of course, but we really don't need to win every single League game to go deep in the competition - we saw it with PSG last season. I definitely feel that if we get a few wins under our belt early then we could rotate a bit - not a "League Cup match against Swindon" kind of line-up, but we might see the odd match where Guehi and Konaté could partner each other rather than Van Dijk always playing.
Indeed, when it comes to League Cup and FA Cup matches this season, I'd be aiming to keep Virgil away from them until semi-finals sort of stages of we are lucky enough to get that far. We have a finite amount of time left with Van Dijk and Salah at the club, so should really try and pace things that we can give them the best chances to lift the two trophies we value most.
Anyway, with that in mind, having Guehi come in and having Konaté for one more season at the same time is something that wouldn't really surprise me. As much as I normally prefer to receive transfer fees for players, I don't think we can necessarily afford to be giving Virgil a new centre-back partner for maybe 45+ matches of the season with all the change we have made already, if we have serious ambitions of defending our title and reclaiming Big Ears.