This isn't really a big deal, but it doesn't give a predictive income for miners. If the early Satoshi coins are recycled during one year, it will be an enormous boost for miners and then a gradual drop. There is no reason to have such an irratic payback curve. People would invest in rigs like crazy that year and throw the rigs in the garbage the next year.
Fixing the transaction issue can be done by either increasing the transaction costs, or as a general tax, called demurrage. This depends on whether people think it is ok to have "freeloaders" own bitcoins without paying for the maintainance of the network, or not.
IMO it would be predictive income. In 100 years we would know exactly how many coins will be recycled and there are many many different ways the coins can be recycled to address these issues. One method would be to base the number of coins recycled per block as a % of the transaction fees included since that will be the only block reward in 100 years. So for example if it was 10% and there are 10BTC in transaction fees included in a block then an 1 additional BTC would be recycled. That would make the increased block reward very predictable and stable. That's just one of many different ideas...Fixing the transaction issue can be done by either increasing the transaction costs, or as a general tax, called demurrage. This depends on whether people think it is ok to have "freeloaders" own bitcoins without paying for the maintainance of the network, or not.
X should be minimum 75 years. That's 1 life 
I agree, I think 100 years is good since it should be > 1 life 