PHP on Marketo

Short answer: No

Longer answer: that would be a security nightmare. 
The risk of SQL injection and other exploits is significant.

To the best of my knowledge that is not in the road map.

BGOmes,

There's risk of SQL injection and general security regardless the technology, so that cannot be a reason..

If the question is related to templates of landing pages - the best you can do is to include JavaScript which talks to services on your web site, but straightforward php won't work for many reasons.

If the question is related to mail templates, then this is really not and would never be possible.

In case you want to have some really special logic in the templates - go with pages directly from the web site and don't bother with landing pages in Marketo. You can still have your Marketo forms on these pages though. 

I am not going to feed arguments regarding security. That is not my goal participating in a community.

My point is: it is far easier to exploit security vulnerabilities using a server-side language (PHP included) than using HTML/CSS/JavaScript.

Anyway, the choice is not allowing PHP is set by Engineering, a group I am not member of therefore I am not in position to discuss the reasons for their decision.