That depends on how much consolidation people opt for. At full consolidation (2048 ETH), we can shrink the 1M validator set to ~15,625 validators. This assumes every validator is staking exactly 32 ETH, so 32 * 1,000,000 = 32,000,000 ETH / 2048 ETH = 15,625 validators.
@vbuterin has mentioned the possibility of a higher 4096 ETH limit for the maximum effective balance elsewhere, so that number could well reduce. The question is whether people will opt to fully consolidate, consolidate smaller amounts (e.g., consolidating four 32 ETH validators to create a 128 ETH validator), or consolidate at all.
But if we have enough consolidation, the need for an active validator cap reduces. AFAICT EIP-7251 was proposed to validator set capping + rotation and reducing stake rewards to disincentivize staking (both of which are controversial and have edge-cases). I published an analysis of EIP-7251 if you’re interested in reading through!