ergophobe - 6:33 pm on Apr 4, 2013 (gmt 0)
>>if I would need to change file extensions
As Lucy said - no. If someone tells you that you do, find a new consultant.
>> if the Joomla platform allowed for files which have server-side includes.
I would have to say no. I mean, maybe you could, but I don't really see how. Joomla is going to want to build the whole page.
But keep in mind, whether you use SSIs and whether you have to have a certain URL extension are completely different questions. I can put any extension I want on my URLs and have them run with just about any technology out there.