With all the time/effort Salesforce has put in to SFDX and the VSCode plugins releasing an APEX compiler must just be completely off the table. I do a lot of Salesforce work and introducing new developers to the SF way of doing things results in a lot of "wut." facial expressions.
In a previous company, we'd have people making direct edits in Salesforce. We'd then export the edits with the Salesforce CLI "force" utility, bring it into a local git repo, run some rather buggy scripts that would change the object namespaces/prefixes to a generic prefix. Then you could finally do a diff and a PR in a normal way.
We then had other scripts that would take the "generic" code and change the namespaces/prefixes for upload into QA or prod environments. It was quite painful.
