Does anyone know if there is any implemented limit to the number of replacements in RBF? Or is this also up to each full-node the miner used for mining the corresponding block and there is absolutely no upper limit for the number of RBF replacements? I vaguely remember reading something about this somewhere, but I can't find it anywhere.
There is no limit when it comes to consensus rules. Miners can include any valid transaction in the blockchain, even if they invalidate thousands of unconfirmed transactions by doing so.
But according to BIP125 (which is a policy and not a consensus rule), nodes accept the replacement transaction if the number of transactions that would be evicted from the mempool by doing so doesn't exceed 100.