Yes, it would. None of the unobtainable items are custom content, while all your suggestions are.
Regarding the suggestion overall, this is just a rehearsal of older threads. In the end of the day the truth remains that the content is readily available, gets a small window that tries to promote it and already has a best-in-slot piece of gear gated behind it, yet people prefer to skip that item or get it with Coins where available. For any regular person that screams major lack of interest. 3v3 is a niche format just like 5v5, the vast majority of people have zero interest in the hassle involved in putting together a team that has synergy and can work well together, much less in keeping it going long enough.
It also doesn't lack "visibility," I can't picture a single serious PvPer who would go surprised Pikachu at finding out it exists. What it lacks is people interested, like has been the case for years and years, and that simply isn't something we change. People like what they like, have fun with what they have fun, and avoid stuff that they will see as stressful. Even more exclusive rewards would, if successful, just add some more teams who would ditch it again as soon as they got the rewards they wanted - as already is the case with the shoulders.