Tough question. There are several "features" of bitcoin that seemed good ideas at the time; but now, in hindsight, they seem to be mistakes, and Satoshi himself would probably agree.
So, one problem that would have to be fixed is making it unappealing to hoarders and speculators.
so make it a bad investment?
Then the value of 1 coin would be determined by its use for e-payments, according to the money velocity equation.
thats basically how it works now. people buy bitcoin for that the market feels it is worth. economics 101
Another problem is ensuring that its value stays in a bounded range, so that ordinary payments can be expressed without too many zeros before or after the point. Say, between 0.01 and 10 USD. In the first extreme case (about the value of 1 yen) one would not need decimal fractions, and do all accounting with integers. In the second extreme case, one could truncate after 3 decimals (i.e. use the "milly" as Americans use the penny).
do you mean to keep the value low such that people dont need to use "mBTC/uBTC/satoshis/etc"? Most bitcoin software allows you to send payment in mBTC or $USD (converted to BTC value). having decimals is not a bad thing, and if that is a problem for some people even when thier wallet software does the 'mBTC/satoshi' conversion its an issue of ignorance.
A stable value would seem to attract hoarders and investors, but hopefully the two goals can be achieved with built-in demurrage (negative interest). Namely, each UTXO loses value at (say) 2% per year, so you can spend only 0.98 BTC of that 1 BTC that you earned 1 year ago. Those 0.02 BTC would implicitly go to the "Bitcoin Treasury" and would be redistributed as block rewards (so the block reward could remain constant forever while the total amount of coins in circulation would still be bounded.)
you already pay fees like this via transaction fees and via the network currently inflating at ~12% (dropping to 6% next year). The concept of 'inactivity fees' is sheer insanity and does nothing but make miners rich like bankers.
Hopefully that negative interest would be enough to dissuade hoarders and speculators.
again, you talk about making bitcoin
unappealing so that it is not desirable as a store of value, why?
Another problem is the centralization of mining. That could be fixed by keeping the block rewards too small to make mining into a profitable industrial activity. But that may conflict with the need to put more coins in circulation as adoption grows.
when block rewards are low, bitcoin becomes MORE centralised, because only those with cheap power can profit. home users are squeezed out by residential power rates and you're left with only datacenters that get power for <$0.05/kwh. your 'solution' would serve to drastically centralize the network by pushing out the small-scale miners
There are also non-technical problems like anonymity, non-reversibility, lost coins, legal jurisdiction, ... but each would be a long discussion in itself...
anonymitity is a problem? or is the problem that anonymity only goes as far as methods used by the user (such as mixing)
non-reversibility is a fundamental concept of bitcoin. As is the ability to lose coins (or rather, being unable to forcibly remove coins from an address you don't control).
with respect, many of your ideas to improve bitcoin fundamentally damage its functionality and value