Making a tag that is not trackable is currently as easy as flipping a bit in the BLE advertisement. The same message is broadcast to all phones, but yes, a tag could also produce multiple identifiers and evade detection. [2]
[1]: Section 8 of "Abuse-Resistant Location Tracking: Balancing Privacy and Safety in the Offline Finding Ecosystem". https://eprint.iacr.org/2023/1332.pdf
[2]: "Track You: A Deep Dive into Safety Alerts for Apple AirTags". https://petsymposium.org/popets/2023/popets-2023-0102.pdf
https://github.com/seemoo-lab/openhaystack?tab=readme-ov-fil...
Seems like in theory you could do that, though there are definitely heuristics you could apply to detect those tags, depending on how stealthy they are being.
Also on the servers side Apple could just limit you to a reasonable number of tags.