I feel your pain. Our users have requested this as well in some cases, but the answer is that it really depends on the particular entities and relationships that are active on any given form...we are lucky because we have a separate project contract for each project, so in some cases we were able to just show the contract description which works for us, but that is available in some lists but not others.
We have also sometimes extended the Tool Tip, which you mention, which is really called the "Enhanced Preview" -- extending this is a lower effort, small dev that has major impact since it will automatically work almost everywhere on every form where the field/record it applies to is in play. The Enhanced Preview for the Employee record, for example, is very rich, and folks kindof automatically know how to use it. We have done the same for several other records for our users when it would have been high effort to add fields into entities or forms.
And, agree with Andreas, we have also in several cases had to address these type of requests with reporting...this can be a bummer since native forms and lists can feed Tiles, etc etc, are closer to the action. But reporting options are also flexible...it all depends on your users.