Does this exist: flatpak-like sand-boxing with gentoo-like source-based package management?

I assume it doesn't, but thought I'd ask.

I really like the principles behind both gentoo and flatpak, but right now I can only do the gentoo way or the flatpak way (and I've opted for gentoo's for now).

What I'd love to have from flatpak:

• container like sandboxing and isolation
• customizable sandboxing and permissions

What I'd love to have from gentoo:

• powerful build system building packages from source
• global declarative management of compilation options
• easy patches
• easy to add packages that aren't in repos
• support for many architectures or setups