I think TurboTax will tell you to file an extension.  However, that is unacceptable to me.  What I don't understand is that last year I filed Form 8903 using TurboTax Business on Feb 18, 2017, and it does not appear that the form has changed.

Same here- TOTALLY UNACCEPTABLE.  IRS.gov says the FORM is still Rev2010 and ready to use for this year.  I have used Form 8903 for years in TT without this issue.  Get on the ball TT and let your CUSTOMERs file their taxes by the deadline.  Telling your PAYING customers to file an extension for something already available at IRS.gov is BOGUS!