Once you hit the hard limit of 1MB constantly for every block, there will be competition to be included in blocks and drive up fees.
A hard limit is not necessary for competition. The reason there is only a little bit right now is because transaction fees are so small compared to the block subsidy that miners don't have much incentive to be selective.
You also can't predict with certainty how far users will be willing to bid up the transaction fees. We know how much they are willing to pay now. If future users are unable to get their transactions in a block they
might be willing to pay more, or they might decide
not to use Bitcoin at all. You can't take demand for granted. Right now Bitcoin is attracting new users because the advantages it offers, but anything that reduces the value proposition reduces the number of people willing to use it. How many businesses maximize their revenue by intentionally limiting the number of customers they service and refusing to increase production to meet demand?
Based on the facts we have available we know Bitcoin users are willing to pay 50 BTC per day in transaction fees with 250k blocks. Right now the number of transactions can only increase by a factor of about 4 before the block limit is reached. At this point we can only process 7 tps no matter how many people are trying to use bitcoin. Assuming that the world-wide users of Bitcoin will happily accept this situation and try to outbid each other to get their transactions included instead of just giving up on Bitcoin entirely is extraordinarily dangerous.
The idea that you can preserve the decentralized nature of mining with a hard cap on the transaction rate is insane. Once the blocks saturate and you get price discovery for transaction fees, then the total mining revenue will reach its maximum possible value. After this point the block subsidy will decrease, and the fee revenue will remain constant. Assuming Bitcoin remains in use after this point there will be no incentive for new miners to enter the market. Mining will slowly get less profitable over time so existing miners will slowly drop out until only a few are left.
Nice job preserving decentralization.