At some point won't you run into IP issues with the ARM SoC? Plus how would you deal with things like power analysis attacks that require modifying hardware to fully mitigate?
ARM IP is bought by the manufacturer of the device, in this case Silicon Labs.
What IP issues can you imagine happening considering ARM SoCs are the most widespread processors in existence with many, many different manufacturers?
Regarding side-channel attacks such as you mention, all processors are subject to this vulnerability to various degrees. Do not expect a project such as this to have any mitigation for that type of attack.
