R devel - Oct 2019 - interception of expression evaluation. What is the right way to proceed?

Hi all!

I am a computer science lecturer at IST (www.tecnico.ulisboa.pt) andhave 
been developing a voluntary computing environment for R together with 
some students. The idea is to allow R users to share their CPU time in 
the community. Both for security of the volunteers (to create a sandbox) 
and for debugging support, we have extended the R interpreter with a 
small intervention in the eval function.

My question is the following:

- Is there any way to transparently intercept all expressions in the R 
runtime? and in a way we should not have touched the internals of the 
interpreter..

- If changing the interpreter is the way to go, what is the correct way 
to propose this change to the R community?

 ??? Thank you for all help,

 ??? Best regards,

 ??? ??? Jo?o Garcia