Yes, stored procedures are certainly an issue which generates some debate in database circles - I suspect it probably depends whether you're used to a database being wrapped in an abstracted API which is considered "part of" the database to all intents and purposes, or whether you regard the database engine itself as a standalone component. It probably also depends to some extent on whether you regard the SQL language as something to be admired or tolerated... (^_^)
However, whether stored procedures are a Good Thing(tm) and whether they should be supported by a shared hosting service are almost orthogonal questions.
I'd say a "traditional" (for want of a better term) view of relational databases would regard stored procedures and triggers as being not too far behind foreign key constraints and transactions in terms of importance. A more "modern" (not to imply better or worse, just originating more recently) approach might consider that the database should be more lightweight and more work moved into the business logic, to ease the complexity of schema updates on horizontally scaled systems. I regard this as a small step on the path which eventually leads to NoSQL and the like.
I guess the nirvana of shared hosting would be to support as many approaches (or "paradigms" if you're making a sales pitch) as possible, so I guess it's a case of weighing up the potential benefits of stored procedures against the difficulty of getting them working securely and reliably on a scalable shared hosting architecture, and then prioritising the feature appropriately. It'll be interesting to see how it fares!
Of course, I'm sure NewSQL is The Future(tm) and will render everything else obsolete in a few years anyway... Well, at least until the next buzzword de jour comes along. (^_^)
Happy New Year everyone!