Why are these options mutually exclusive? Is there some technical limitation here preventing us from having one monotonic clock and a separate orbital clock?
The UNIX 'zoneinfo' format is flexible enough to incorporate second offsets, so this can be done on many systems today (Linux, *BSD (the latter including, I assume, OS X)).
The system clock would be kept in TAI (or maybe GPS, which is a fixed number of seconds different than TAI?) and the local time is calculated by applying a timezone offset in seconds.
Given that the leap-second problem exists, this is the right technical way to deal with it. Unfortunately I've never seen anyone doing this, but they should.
(Of course it'd be ideal if humans were willing to abandon their silly timezones, and just plan schedules in absolute time that made sense for their geography. Alas, not sure we're ready as a species for this level of change.)
Both of those already exist, and in fact the GPS system uses the orbital clock, for obvious reasons. People are arguing about the default... always fruitless.
/* Urbit time: 128 bits, leap-free.
**
** High 64 bits: 0x8000.000c.cea3.5380 + Unix time at leap 25 (Jul 2012)
** Low 64 bits: 1/2^64 of a second.
**
** Seconds per Gregorian 400-block: 12.622.780.800
** 400-blocks from 0 to 0AD: 730.692.561
** Years from 0 to 0AD: 292.277.024.400
** Seconds from 0 to 0AD: 9.223.372.029.693.628.800
** Seconds between 0A and Unix epoch: 62.167.219.200
** Seconds before Unix epoch: 9.223.372.091.860.848.000
** The same, in C hex notation: 0x8000000cce9e0d80ULL
**
** New leap seconds after July 2012 (leap second 25) are ignored. The
** platform OS will not ignore them, of course, so they must be detected
** and counteracted. Perhaps this phenomenon will soon find an endpoint.
*/
There is no "0AD", and if you don't have leap seconds then the number of seconds per repeat of the Gregorian calendar is not fixed—just have a look at the graph at http://www.ucolick.org/~sla/leapsecs/deltat.html
TLDR: if you define a bunch of complexity into your definition of time, you'll have a very complex model of time.
Eg, if you define the Gregorian calendar as a function of the position of the planets, rather than a function from atomic-clock seconds to a string, then the Gregorian calendar is not fixed. I suppose Pope Gregory designed it as a function of astronomy, so who are we to roll our own?
Yes, this equates to TAI minus 35 seconds. GPS did exactly the same thing (instantiated at a TAI offset equal to UTC), perhaps in a vain hope that the astronomers would give up their death-grip on time. Not sure the difference between 35 and 19 amounts to "rolling your own."
(At least future decisions are out of the hands of the astronomers and into the hands of the timekeepers, so maybe these responsible authorities will just refuse to declare further leap seconds regardless of heavenly tantrums.)
The comment just describes a trivial notation for representing 128-bit TAI as an unsigned integer. The closest comparable "standard" that I know of is DJB's TAI64 [1]. (Everything released by DJB should be regarded as a standard.) But TAI64 is (a) defined as a bytestream, not a uint128_t; and (b) has a hopelessly complicated fractional subsecond system.
This scheme is different due to the way it handles times between the start of leap seconds and 2012.
And, as an astronomer turned technologist, I think your comments are completely inappropriate for civilized discussion. If you want verbal mud-wrestling, take it elsewhere.
The system clock would be kept in TAI (or maybe GPS, which is a fixed number of seconds different than TAI?) and the local time is calculated by applying a timezone offset in seconds.
http://www.ucolick.org/~sla/leapsecs/right+gps.html