If there is going to be a community maintaining binary artifacts containing boot chains on LVFS then there should be a single definition of those boot chains, even if the boot chains are not uniform (i.e. use different firmware and image containers). Ideally, that definition should exist in a large well maintained community based project.
A open boot chain is a biased towards vendors that are relatively transparent about their boot ROM interfaces and have less complicated interfaces without hidden or proprietary firmware. Intel/AMD x86 and Qualcomm/Apple aarch64 are examples of the opposite, while companies like TI and some MediaTek SoCs that target embedded use cases are more transparent, with documentation that requires a business relationship, but not on the same level as other vendors. Therefore a focus on embedded makes a complete boot chain much simpler. Buildroot is focused primarily on embedded targets.
Buildroot is a long-running well-maintained community-based project that includes support for dozens of targets and the ability to use custom or pre-built toolchains.
Additionally, Buildroot has minimal host dependencies (see Chapter 2. System requirements.
Unlike some build systems it does not require virtualization nor does it depend on containers. Compared to running on the host, VMs/containers require moving data in and out of them, do not have the same tools as the hots (e.g. system vs. application containers, or don't match the host distribution or user's preferred tools), and require special knowledge to debug.