Personally, I'm indifferent about the addition of non-pony, given that we are a fandom with many crossroads. Myself, I came into MLP from TF2, and then found interest in a variety of new things, from Wander Over Yonder to the Count of Monte Cristo (and Jekyll and Hyde for good measure).
Granted, BronyCon stands as the most famous pony conventions in the US. If they add too much non-pony, then BronyCon essentially becomes another generic convention. If anything, I see the staff of BronyCon attempting to augment the essence of what made this convention so popular with new, fresh material.
In respect to vendors and what I understand, the process to get a booth to setup in is already iffy enough. If there is to be more diversification in this con, I feel as though the marketplace needs free up more space for booths to help ease the strain of booth application. Perhaps there can be the opening of a secondary market, the main one being the Vendor Hall, and the being the Artist's Alley.
I personally would divvy it by the nature of products sold.
"Handmade goods" - Items made by artists, not by licenced companies, (Enterplay, Aurora, 4de, etc)
Custom Plushies, Clothing, Jewelery, Accessories, Dishware, etc
Prints, Posters, Wallscrolls, Linens, Soaps, etc
"Collectables" - Official Licensed Merchandise (MLP or Otherwise, Just Licensed)
Trading Cards, Play Mats
Accessories (such as those Dog Tags)
Hopefully my thoughts will help. If not, please offer constructive criticism. Thanks.