You have to remember that a doctype is, essentially, the set of rules you are telling browsers you are using to create your markup. You cannot/should not change the rules mid-stream. You never try and make the doctype fit the markup but the markup should always match the doctype.
So, if you can't get your markup to work with a certain doctype, fix the markup and not the doctype. All new pages should always use 'strict'. There is no need for transitional (for newly marked up pages).