I cannot even up vote any of the suggestions on this site, the make over is terrible. I am a long term user and these are essential things prime need to do now:
Allow custom functions to be developed using .NET framework - c++ is out of date and mainly useable for gift level computer programmers. This is ridicullous.
Expose more in the prime API such as ability to access and modify tables in mathcad, ability to access nested arrays. Ability to access regions in mathcad through API.
Allow user to supply a variable when referencing paths to worksheets. Ridiculous how many times my references are broken and a user can not explicitly assign volume, global path.
Ability to add user defined functions to be accessible in a tool bar search list as per built in functions - same for custom functions.
Improve the performance of look up and other bottleneck matrix built in operations like stack, augment, match, vlookup
Ability to create ebooks or navigate to regencies sheets easily.
Ability to allow a worksheet to be condensed to a function say through user assigned input and output variables - This to me would be huge and a real game changer.