Nit: Just MIT

Just copying it from main.cpp, where the code came from. If you want it changed here, make a convincing argument to change it there first.

All files need changing, but instead of doing it all at once, we're just changing it as files are updated. Please use just MIT.

This has been discussed already. I though we had merged a PR changing everything to just MIT already.
That would be simpler than warning people every time they copy the license from an outdated place.

Why bother with fRateLimit/fLimitFree at all here, since the logic boils down to:

fRateLimit = !fLimitFree ? false : false

You could just write:

if (!policy.AcceptMemPoolEntry(pool, state, entry, view, false))
    return false;

if (!policy.RateLimitTx(pool, state, entry, view))
    return false;

Is it the idea that more behaviour will be added here or?

Not all transactions should be rate limited, for different reasons, some of which are policy (contracts with retailers?), some of which are not (local user manually wants to broadcast a transaction).

Notice fRateLimit is passed to AcceptMemPoolEntry by reference, and it may (and does in some cases by default) change it.

Right, the pass by reference was what I was missing. LGTM then.

I agree this feels confusing. I wonder if it ought to be moved onto CValidationState so any step of the process can set it?

Why do we even need an object for policy? isnt it all static?
Maybe best to just do a Params()-style Policy()?

A params-style global hidden behind a function you mean?
I prefer a class.

@TheBlueMatt It isn't inherently static. It might be nice to one day have nodes with multiple policies, using different ones based on transaction sources and mempools...

I don't think this should be called here. This should be in policy.cpp and the field in Policy is not really required.

This has to be called here. When CNodePolicy is initialised, Policy() might not have been yet.