Why would we ever need 10k new addresses in average per day?
Bitcoin transactions usually carry change, and to increase privacy and security, it is certainly no worse to generate a new address every time for receiving change than to reuse old addresses. Details maybe belong into their own question; however, it is well within the realm of reason to expect a future where most Bitcoin transactions include two new addresses (one for the person paid and one for the change back to the payer).

If we dream up a future where arbitrarily small micropayments can be handled by Bitcoin, then I would actually call the 5k transactions per user that could hence generate 10k new Bitcoin addresses a vast understatement of the potential. I'm thinking that rather than paying my mobile carrier for data roaming, I'd want to use micropayments to pay for routing of IP packets in adhoc wifi networks (ok, maybe not for each individual packet given the overhead---but I could, from a user's perspective, want that to happen for every 10 kb chunk of data or so). And I can envision much the same thing with my regular ISP, or even with most websites I frequent (and, come to think about it, maybe some of them should pay me).

The problem with this is that all these transactions end up in the blockchain, occupying a huge amount of disk space. That is why many suggest that micropayments ultimately belong off-blockchain, meaning some other solution should be found for them that does not place the burden on Bitcoin. In my example, it is easy to see why this is necessary: Even if only 100 nodes kept the entire blockchain, then my 10 kb chunk of transmission data would occupy much more than that in distributed blockchain storage just to finalize my payment for it. Obviously not just inefficient but truly unsustainable at scale.

Hence I would say that as far as Bitcoin's blockchain is concerned, we need not worry about seeing quite that many addresses added to it. But if whatever off-blockchain solutions we will adopt for micropayments in the future uses Bitcoins' address scheme as well, then we may well, outside the blockchain, envision such a massive use of Bitcoin addresses.