I roughly remember that conversation with @gstolz. ^^
But it’s correct that we do not have any concrete plans to have a Linux compatible plugin for mssql at the moment. That’s, because database monitoring is a big topic in general and also in some sub parts (e.g. the mentioned one), but currently not directly on our roadmap.
It’s a big (sub) topic, as it makes no sense to increase the number of plugins, that need to be maintained in two versions. Instead, it should be one single plugin or – at least – share a common library.