One thing I'd like is for there to be the number of stages per frachise to be proportional to the characters. Like 4 mario chars = 4 mario stages not 6 while Star Fox has 3 chars and 1 stage
Yes and no. New stages are usually proportional to characters, but they are also, generally, proportional to the amount of new titles released in the interim between the previous Super Smash Bros and the current.
Brawl: Delfino Plaza (Mario/Super Mario Sunshine), Luigi's Mansion (Luigi/Luigi's Mansion)
SSB4: Starship Mario (Mario/Super Mario Galaxy), Luigi's Greater Mansion (Luigi/Luigi's Mansion 2), Bowser's Castle (Bowser/New Super Mario Bros), Rainbow Road (Peach/Mario Kart 7)
Although Sakurai also throws in stages from older games for good measure, but for the most new games tend to influence stages along with which characters are added. I have also observed that home console game series tend to be more apt to receive a stage than portable series.
Overall, stages should not be restricted to the number of characters, otherwise you miss out on great stage opportunities.