I'm glad you are interested. Obviously, you cannot switch from IPB just yet, but make sure that before you do, you test alphaPORTAL, etc. and make sure it is what you want. I would hate for you to have to switch back because it isn't what you expected.
Second, alphaPORTAL is not yet stable. There are a few bugs still (mostly the ones relating to the Posts Anywhere MOD - Ones I cannot control too well...), but I am working on making my own Posts Anywhere function, adding on to how Handyman already has his MOD. I was thinking of making my own completely, because then I don't have to link him with credits, etc. however, I decided that I liked his ACP module a lot, so I'm going to try and make the frontend work how I want it to.
Please also note that you shouldn't blame Handyman (the author of Posts Anywhere), because these bugs are actually me trying to utilize features not yet implemented
About the subpages, i'm going to explain how they work...
You make a category. That category is now a "page" with no content. You may put categories under it, thus making "subpages", or you can modules, or both. If a page has no modules, only subpages, you are automatically sent to it's first subpage, making it easy to use a page as a category with no content, just pages underneath it.
Now this is all great, but what about what you are asking? So, to answer your question, you can use the Portal module to show any given post in a custom page.
The easiest way to see how alphaPORTAL works would be to install WAMP (for Windows), or MAMP or LAMP (for Mac and Linux), then testing it out. However, if this is out of the question, I'm going to upload a few images...