what are limitations on moving a show file from one EOS device to another. I have a showfile from an ETC Element 40, are there any limitations / problems to opening that show in an Ion or any other EOS console?
Going up from an Element to and Ion or larger (Geo@5, Ti, etc), no problem, it will work fine.
Coming down to an Element from a larger console, you will loose any additional Cue lists in your show as the Element (and Element 2) can only have one Cue List. Beware or any large differences in software versions as well. Elements running software older than 2.7.0 lose a lot of features. The following are a few other things that will happen: https://support.etcconnect.com/ETC/Consoles/Eos_Family/Software_and_Programming/How_Element_Compares_to_the_Other_Eos_Family_Consoles
Moving a showfile from Eos to Element
Note that the showfile that you open on Element is not changed when opened. The showfile is loaded into persistent storage, and that copy is changed. Data that is removed or changed will affect the show in persistent memory and any subsequent saves of that showfile.
Other than moving up from or down to an Element there are no restrictions moving from one console type in the EOS range to another, other than the total output (address) count of the console in question. You obviously cant move a show with 10,000 output addresses down to a console that isn't licenced or isn't capable of handling that many outputs without losing something.