Was Sarcomite Myr considered for Phyrexia All Will Be One?

I think it was talked about.

Is Sarcomite Myr more likely for a reprint now that colored artifacts are more regular?

Sure. It would need to be on a world with Myr.

Myr have appeared outside of Mirrodin, before. Brudiclad and Sarcomite Myr exist in Dominaria in an alternate future. One that sounds a lot like New Phyrexia reinvading Dominaria, by the way.

Futureshifted cards in Future Sight are not necessarily set on Dominaria.

You've said that you want to do contraptions exactly as worded on steamflogger boss... But future sight was riddled with things that ended up being done similarly but not exactly (tarmogoyf ~ Delirium boosters, sarcomite myr ~ esper shard, ghostfire ~ eldrazi, lucent liminid ~ nyxians, virulent sliver ~ infect). Why are you making Steamfloger Boss completely immutable while you solve contraptions? Isn't this just making something (that matches exactly) simply to show you can (bad design)?

Doing it in the very next set regardless of whether it fits or not is doing it to prove you can. Waiting for the right spot to properly solve it, is good design.

Is Lucent Liminid sort of like Nacatl War-Pride, Ghostfire, and Sarcomite Myr in that it represents a card that could have been from a future set, but the set took a different direction?

Not every Future Sight timeshifted card 100% captured the future it hinted at. Some showed one aspect that got used while including other aspects that didn’t. 

Sarcomite Myr seems to be the preview of future sight for the Scars of Mirrodin block (please correct me if I'm wrong) if so is there a reason it wasn't reprinted within the Scars block?

Future Sight cards often hinted at sets without necessarily being in them. We did try to work it in but it never quite fit.

Was Sarcomite Myr a foreshadowing to the most recent expansion? Will Steamflogger Boss ever get his buddies or is that a question that will need patience to be answered?

Sarcomite Myr was a flavor foreshadowing of Scars of Mirrodin block. The creative team chose to flavor that card because the mechanics felt like they could go into the set that returned to Mirrodin. An earlier set needed to use the new mechanical space (Esper in Shards of Alara) so when we actually got to Scars of Mirrodin the card didn’t fit mechanically. We did spend some time talking about printing it anyway, but in the end, felt that we should only use the future timeshifted cards when they fit just right. As for Steamflogger Boss, there are no immediate plans but I’ve learned to never say never about future designs.