Question
I wonder if ASPX + Portal on the same website is officialy supported, using Kentico 11 CMS.
Research
Documentation states, that:
If required, the Portal Engine and ASPX Templates models can be combined on a single website. For example, you can place pages using ASPX templates onto a portal engine website, and even insert custom ASPX pages implementing your own applications. On the other hand, you can create ASPX page templates with areas that can be edited through the portal engine.
On the other hand, only these modes are listed in the officially supported section:
Due to this I'm not really sure how the thing is.
As of this post date, Portal + ASPX is still supported in v11.
BUT if you want to keep up with Kentico and where the market seems to be trending, you will move towards MVC. Take a look at Kentico's Roadmap, it's clear they are taking an MVC first approach.
If you're not sold on MVC yet and considering ASPX, I challenge you to take a hard look at that and ask yourself why. Anything you can do in ASPX can be done just as easy in Portal with webparts and/or global handlers/events.