We are almost finished with our new consensus model that uses activity as the main metric in block rewards.
Conceptually, is there any reason that staking needs to be part of the consensus model? Our goal is to be even MORE egalitarian than NEM and allow participation without a minimum staking requirement
You need a "scarce" resource as a replacement where it's not too easy to game the algorithm. If "activity" is the transaction rate, then I think your concept is flawed. While it may make sense to restrict transaction rate (like Bitcoin does with its [post-segwit] 4MB blocks and other coins with a transaction limitation) and make transactions "scarce", the problem is that the "currency validators" and the users are competing for block space. Thus, the coin will run into scalability problems much earlier than Bitcoin.
It also isn't egalitarian at all, because the nodes that will benefit most are big exchange nodes with lots of transactions. That can be positive for a small altcoin where it's essential to get some services (exchanges, wallets etc.) on board, but in the case of a bigger cryptocurrency it makes an exchange hack very, very dangerous.