Reducing Number of Fields in Content Type
This is really interesting and, whereas the suggestions in the other question are really good as pointed out by the comment above, I don't really think it's practical to give up on the Field UI for this (like mentioned in the other question).

Let me explain:


Creating a custom field is really easy, there's a good example in Panopoly Widgets for the dashboard widget, which has a custom field for the Spotlight widget.
Creating a custom entity isn't so bad either but creating every single field using Form API should be out of the question


The only plausible solution that I can think of would be to implement hook_field_storage_info() and create a new Field API storage backend that uses a better table configuration.

If you look at field_sql_storage.module in core, it's a pretty concise module that provides the one field per table storage backend, I'm sure with some hacking around you could create a new backend that uses one table per entity and stores each field in a new column there (kinda like D6 CCK with cardinality 1 fields).

You would have to be constantly altering the table schema whenever new fields are added (which should be fine). This might be the place to do it: hook_field_storage_create_field().

It's pretty theoretical but I think it'll work... the beauty of this approach is that you can still use Field UI for everything as usual.

Caveat: You're gonna have to figure out how to handle complex fields or multiple cardinality (hint: more columns?)

PS - Knowing of the frequent schema changes, you wanna make sure you have backups/concurrency for peace of mind.

Good luck and if you get this working I'd like to see it! :)