It is no secret that Sigasi wants to be Sigasi vs Emacs VHDL mode. I have posted several articles about the fundamental differences between Emacs and Sigasi. It usually boils down to the limitations of regular expressions and pattern matching. There are just certain things that require a parser rather than a simple pattern matcher.
But we have to say that the VHDL Emacs mode has given us quite a bad time when it comes to beating the Emacs VHDL code formatter. For the longest time, we were almost ashamed of the quality of our code formatter in comparison with the Emacs VHDL formatter. Just recently, we have covered that issue too.
What is still missing?
There is an Emacs emulator available for Sigasi (and for Eclipse), so you can keep using your old key bindings. But there must be other things that you miss when switching from Emacs to Sigasi. Let's build a list of (relevant and technical) things that are missing from Sigasi HDT. Please send us an email for the Emacs features you still miss.