Power BI Pro
Does Action Pack provice Power BI Pro Licences ?
If not, does the o365 demo site offer the ability to prototype new Power BI Pro designs and functionality ?
Development Platform & Tools
No, Power BI is not currently included in Action Pack (see https://partner.microsoft.com/en-us/membership/internal-use-software where you can open up an Excel spreadsheet).
Regarding your 2nd question, I'm unable to assist.
This split of functionality and licenses is a nightmare. Office 2019 has different funcitionality to o365 in the cloud or local or Teams. No Power pivot in Action Pack.... Keep it simple and stupid! Nobody wants to spend his time in understanding this differences. Sorry Per, you are probably not the right person to address this complain.