wrefiyu As @Staudey already said, it is very unlikely Solus is going to propose another DE at this stage. Solus is a small distro and what we want to avoid is to get a repository which contains many outdated/unsupported packages.
I have already seen people who are truely motivated and who offers to maintain something but who disappear a few months later because they found something shinyer elesewhere, they got tired of it or whatever and then the team has to take over this additional workload or to deprecate the packages from the repository which from a user experience point of view is terrible, especially for something like a desktop environment.
Gnome, Budgie and MATE are all GTK based desktop, so they share many components which makes it easier to maintain. Plasma was introduced by long time team members.