Rank fallback transport by newest block number

[gndelia]

I'm looking at the docs of fallback transport, and I see it ranks transports for latency and stability.

I'd like to be able to customize the ranking with another criterion: "Latest block number". I'm currently facing an issue in Ethereum mainnet where the default RPC for mainnet https://eth.merkle.io/ is the fastest and stable in answer... but it's lagging behind. It's stuck on an old block number, so the other RPCs are not being used. I'd also like to weigh in the ranking the block number. That could be an option, or another could be just offering a property/method to allow custom rankings, giving the flexibility to consumers.

What do you think?