The main drawback of the trusted setup is that it is not auditable. It makes it impossible to ever know if the setup was corrupted, and if the supply really is limited to 21M.
I think the trusted setup can be made more trustworthy, if there is an open participation, and if there are MANY participants. I already suggested this. Instead of 18 participants or so, you could provide for thousands of participants, essentially everybody who is interested.
A suggestion is this: consider, say, 20 000 participants in the setup (with the idea that less people will actually show up). Ask people on bitcointalk to post their public parameters. Up to 20 000 people can do so before a given date. We can all see those contributions, and YOU can see YOURS.
At the given date, include all the published public parameters in the final trusted setup parameters, and generate as many others to reach 20 000 in total. The only thing YOU have to verify is that YOUR parameters are part of it. Then you know if you can trust yourself.
It doesn't matter if 99% of the others are "Sybil" parameters: your parameter is sufficient to give you some trust in it.
You can also verify that all the published parameters are included. It would be a good idea if people could sign their parameters with PGP signatures, so that we have an idea of the diversity of the number of people involved.
But again, if YOU are part of the trusted setup, YOU can trust it. With, say, 20 000 participants, chances are that many people can trust the trusted setup, and in the end, even people that are not part of it (later) know maybe some people that are part of it, and which they can trust.
Of course, you can never take away the existential doubt of a trusted setup, unless you are part of it and you know it ; but if, say, 20 000 people are in that case, then I think the trusted setup can in practice be trusted.
A few friends and I are considering forking Zcash with a couple small tweaks. 1) address the trusted setup, perhaps by enforcing a periodic coin audit (transaction which reveals not who, but how much owned) at the protocol level. 2) reduce or eliminate the founder's reward. (I'm for eliminating it, but I understand that it's tough to motivate anyone to work entirely for free)
You definitely should eliminate it.
You should also make anonymous transactions compulsory: ONLY notes after the coinbase creation.
As someone said somewhere: if you use ZCASH, it is for its anonymity. But then you should use anonymous transactions. Even if they are "heavy".