It will definitely be more secure, but probably drastically less open, since there won't be any GPL code underneath for people to demand copies of.
Fuchsia, once it reaches the level of polish required of proper Google products, will be as closed as iOS. And security will be the justification for it.
The Fuchsia code itself is open, and while a vendor could make changes and not release them, a project like Pine wouldn't do that. That would indeed be a major motivation to use a Pine-like over other vendors.
For now. It doesn't yet have all of the proprietary bits added in, nor has it been shipped to OEM devices using mobile device hardware. Most of the proprietary Google bits of Android are proprietary by choice, there's no way Google is going to be any more open with Fuchsia.
I disagree. Fuchsia will eliminate the need for the hardware vendor to supply open-source drivers. In this regard, it is a major step backwards in security and upgradability.
Fuchsia, once it reaches the level of polish required of proper Google products, will be as closed as iOS. And security will be the justification for it.