And if you refuse to accept that the optimal solution is impossible to implement, you will forever try to build a perpetuum mobile rather than go with the second-best solution.
Absolutely - fair point and taken. The optimal solution for time & date is probably way beyond SUT: One could discuss months (12, why so), weeks (7, wtf?), days per month (28-31), ... I believe there are many ways to improve our current life. SUT is a humble and very practical proposal, as soon as you accept that standing up is at a different time in Japan than in Berlin.
Give it a try in thinking, you may enjoy the light feeling in your stomach afterwards.
Well, yes, but unfortunately, time is inherently non-metric. As long as we mainly operate on this planet, we have two basic units of time: the day and the year.
Now unfortunately, the latter is roughly 365.24 days, so whatever unit X you choose such that 1 day = 10^n X, one year will be 3.65 10^{n+2} X. Again, there are two choices (as outlined before for the case 86400s = 1d): Either divide the year into some arbitrary months (365 has the ugly property of being 5 × 73) or have stupid stuff at the end (apparently some cultures have 12 months of 30 days each and five special ones). So is it possible to implement a much better way of counting time? Certainly, yes. Is SUT such a way? Probably. Is it worth it? I don’t think so.
(And, again: The matter of timezones is orthogonal to the matter of how you divide a day, you can easily abolish timezones and still use 246060 – you can even do so slowly by using UTC as an implicit timezone with your social circle.)
((As hinted at above, this whole matter will get even more ugly when there are humans on the Mars and Earth – clearly a second (basic SI unit) should be the same length on both planets, but what about hours? Days? Years?))
Thus my approach is to do - time will show if it was impossible or not.