Hi Jamie,
To me this idea that titles should not exceed 65 or 70 chars is just a guideline. I would go by is the title meaningful, is it concise, does it have superfluous words, and if so then maybe it needs to be reduced but I would not otherwise change titles arbitrarily to meet the guideline in absence of one of these more relevant issues. SEO is not the be all and end all reason for making decisions, I would focus more on meeting the needs of the actual visitor than the search bots. But if you feel that users are not making good quality titles, it is also best to give the users some guidelines about that, ie a content style guide or something of that nature might help.
The database field for blog post titles holds 255 characters and the textbox has that as the maxlength. In trying to think of a low effort way to help you I could easily make it possible to override the maxlength on the textbox for blog titles by a config setting so that you could set a smaller limit there if you want to.
Would that satisfy your need? Otherwise more complex solutions that require more work would be very low priority for me vs other things that need to be worked on.
Best,
Joe