I know they're (federated) possible technically. I'm arguing that they won't be necessarily economically viable. Even the SC's Whitepaper warns against their use.
They certainly won't enable the financial success for Blockstream that they seek through the spvp that even you've already admitted to.
Yes, federated models will probably be central to Blockstream business model.
SPVP will facilitate the construction of open-source, public good, platforms/sidechains that will likely be built in cooperation with the community and will allow anyone to leverage their utility and build applications on top of them.
Again, you fail to argue why you suggest they will not be economically viable. SC's whitepaper warning against their use seems to relate to a general concern about their inherent need to rely on more centralized entities.