Hi, Ghadi. The particular exploit, was actually exploiting the bug in the OpenSSL. It was actual bug (non constant-time operation in crypto code) in OpenSLL, that got patched. SMT made it easier to exploit, but even without SMT it was likely it can be exploited.
As of SMT, SMT makes a lot of things easier indeed. It is very unlikely Mill of any kind will ever by SMT enabled, because it would be really hard to do. SMT is beneficial on OOO because it is pretty easy to implement if you already have OOO available. Adding SMT to in-order core, with no OOO is relatively speaking more expensive, and at this point it is often better to simply add more cores for even better performance gain. Obviously SMT is still probably beneficial even on a Mill like design, if the SMT is wide (i.e. 8 way), and the code you are executing is limited by the memory latency. Time will tell, maybe you are better off by using GPU / Xeon Phi like CPU, then, or doing software smt, and try to load as much stuff in parallel, by rewriting the code, or develop SMT enabled Mill, but I am sure this is really not worth discussing at the current stages of development.