Are you really that surprised? People have been asking for more solo-content for YEARS. Like for as long as I can remember. So here you are, finally delivering what purports to be challenging solo-content, and you've decided to limit access to wealth.
And you're wondering why people are both excited for this feature and at the same time frustrated with the design choices you've made?
No, we're not surprised, but World of Warcraft hasn't traditionally been about solo content, either. Really, it still isn't - while you fight alone at the Brawler's Guild, you're surrounded by your peers. It's, at least in spirit, still social.
The whole thing is very much an experiment.
I think it's also worth mentioning that the feedback we're receiving on this isn't being ignored, and that we're still considering alternate methods of distributing the invitations.
I think you will find that the social aspect of it is ancillary to many of the players. What will interest people is the ability to show what they have, individually, in a challenging setting. There's a big demand for that, regardless of a social component. So if this is the outlet you're giving us, that is going to create the demand for it.
Filtering the supply by limiting invitations is consequently going to be frustrating for many players who have the skill to be competitive in this environment, only to find that character wealth, a factor that no bearing on player combat skill, is being used as the litmus test for entry. Frankly, I think you should have to brawl your way into Brawler's guild, not buy your way into it. What would Tyler Durden say!?!
And again, you're only delaying the intrinsic queue issue by gating the invitations. Eventually, the "regular" brawlers will become more numerous and you haven't provided any insight into potential solutions for that.
I have a couple solutions myself.
1) Put several brawl sites around Azeroth. Why need there be only one? Want a shorter queue, fly to Thunder Bluff or Dalaran or wherever. Want more social interaction and observers, wait longer in the Orgrimmar queue.
2) Instanced Brawler's guild. But not individually instanced. Instance it with 5 people. Similar to how and LFR fills in replacements when people leave, BG instances would be a rotating group. You get in, you watch the fights before it's your turn. When you're done, you leave the instance, and the instance invites someone else to watch, from the end of the queue.