Not sure it would be a good idea. Search is usually a tradeoff between relevancy, speed, index time/volume and query complexity ( aka special keywords/filters/options). Making tags part of the directly searchable keywords would hurt relevancy in some cases ( how do you rank a post containing pr-welcome in body versus a post tagged pr-welcome?) and probably hurt performance.
It’s easy to see a query and say this should be first and this second… but once you take all the cases in consideration it’s much harder.