Like I said above, this will be an alt-coin and a hard fork for bitcoin. You'd have to find someone to write the code for you and then convince people to switch to your fork. It seems unlikely people will do so but the new alt-million-year coin would not be bitcoin. Without some clear need it is highly unlikely the developers will code this for you.
All that said, the code itself seems simple based on your description so it would be pretty easy to implement. The issue is convincing people to switch to your alt-coin. I believe it would take a very good reason to get people to do so. Selling it would be something you'd have to do.
Current Bitcoin miners would most likely accept this change because after 2020 they already won't be in mining only for reward but mainly for transaction fees. Its in their best interest to mine as much time as possible for fees and for reward and this change gives them more time after each decrease to do just that. Once the code is written and some developer will think this is a good idea, it will sell for itself to the miners, and it'll sell itself to the adopters that wish for Bitcoin to succeed in the long term. It'll also make Bitcoin truly the gold standard. It'll also make the current developers prove that they've grown up and implement true changes beyond fixing the code at the superficial level.
I don't care about altcoins, I'm an Bitcoin adopter coming with an idea, I wish to see pro cons arguments not suggestions to make a new altcoin. Probably the code is simple but the implications are big so that must also be taken into consideration. We need to grow up, take the initial idea of Satoshi keep all the principles like
preventing double spending, limited supply, medium of exchange, decentralization, POW instead of trust, and build alongside a better future Bitcoin protocol while we still can. I don't think my proposal breaks any of these principles and it benefits everybody involved in Bitcoin in the long term. Once we adopt this gold standard we can be sure Bitcoin will be here to stay for good and its value/price will continue to rise and the incentive to mine will be even stronger because not only you'll mine for reward but also for transaction fees and you'll do that for a prolonged time which is not only in your favor but also to the regular adopters who wish for Bitcoin to succeed in the long run, they'll know that Bitcoin is the gold standard and it will be here for a long long time so like I said the network effect will grow exponentially.
This proposal is based on psychological human factor in which the future generations need to know that they can search for something and get a reward if they'll find it and searching for Bitcoin will give its value and will also assure us that Bitcoin will be considered valuable in the future as well. Time and timing is everything, this change needs to be considered at the next decrease in 2016 otherwise its futile. I'm sure the idea will sell itself once more developers/miners read it, in my mind it makes alot of sense but thats why I make it public so that anyone can come with a con or pro argument.(Hint: I'm 99% sure this won't get implemented and no developer will take the time to really understand it, but really putting it out there is all I can/wish to do)
P.S. Excerpt from Satoshi's whitepaper 12. Conclusions: "Any
needed rules and incentives can be enforced with this consensus mechanism.(CPU Power)" He knew that new rules will be added and as long as it doesn't break the basic principles and if the incentives are there we can make it happen, if not then not, but I'm against doing nothing instead of implementing some huge incentive to us like adopting the gold standard which will make Bitcoin and its adopters more empowered as the search for Bitcoin will continue for a long time, giving Bitcoin a value for that longer, in return giving those who mine/hold/use Bitcoin a better perspective over time.