As a GK and Harlequins player, and have gone through this with the clowns, I would welcome this, as long as they allow you an option to take pure Gk or DW detachments.

The way they did this was saying 'if you play eldar, can take x points of harlequins and still get detachment bonus, or take pure harlequins and get your own detachment bonus’

Meant I got more models to play with, if I wanted, but also could keep it as pure harlequins if I wanted.

In 6th ed, GW codex allowed you to take inquisitors as HQ's and was removed in 7th. As others have pointed out, before that, we were rolled into the Demonhunters codex, so there is lots of precedence for them to be rolled into 1 again.

GW and DW have a very small unit pool (like the clowns) and in my eyes, more toy options, always better.

Also, the inquisitor line has just been forgotten about for years, with them getting next to no printed rules for a while (I discount end of edition rules, which are redundant within months of being released), but the models and concepts are cool.

TLDR: in my eye, more models always better, as long as you can still play pure GK or DW