That is I guess at least theoretically possible but objectively not currently happening and miners have every incentive to include them as they can extract extra revenue from the MEV opportunity this presents. In order for that to theoretically happen you have to assume every miner will be economically irrational. Most miners and thus most hash rate currently accept out of band transactions. There are collective out of band systems like the mempool accelerator and mining pool specific ones such as those by Mara and ViaBTC.