It's mentioned in the Alloy of Law that Miles Hundredlives has gotten in the habit of constantly burning gold. When Spook constantly burned tin, he became a tin savant. Does this mean Miles became a gold savant? If not, shouldn't he have?
In my opinion, the answer is yes. At several point the book comments on how it would be very dangerous (possible even lethal?) for Miles to stop burning gold at this point. His body seems to depend on the gold to continue working. My personal interpretation is that the gold given regeneration has totally superseded and replaced the normal healing and regeneration processes of the body.
Also note the fact that Miles no longer feels pain. His body seems to have been quite significantly changed from the human norm. He is at least as much changed as Spook was.
Let us define a savant as someone who has been altered through long use of Allomancy or Feruchemy.
The bullets ripped through Miles’s body. Marasi watched, holding her breath, forcing herself not to wince. It was time to stop being a child.
He was shot again. Her eyes open, her nerves steeled, she was able to watch with horror as his wounds started to heal. It should have been impossible. They’d searched him carefully for metalminds. Yet the bullet holes pulled closed, and his smile widened, his eyes wild.
—The Alloy of Law
Brandon Sanderson is notorious for having highly predictable magic systems. Many times, the slightest clue in one book demonstrates a detail about the magic system that will not be revealed until an entirely different series.
In this case, Miles kept healing after all visible metalminds had been removed. Marasi believed that he must have secreted away a metalmind somehow, which he was using to heal himself. But her incredulity suggests another explanation: Miles had been so altered by constantly compounding that he will continue to heal briefly even after being separated from his metalminds.
In fact, the author later confirmed this reasoning and explicitly indicated that Miles's being a savant was why he could continue healing briefly even without metalminds.
Questioner: There are Allomantic savants, are there Feruchemical savants?
Brandon Sanderson: Much harder to do. My feeling on Feruchemical savants was because it was your own power in the first place, you can't steep in it so much in the way. But, if you can get someone else's power or if you are fueling your Feruchemy another way, you would become one. So, the Lord Ruler is a good example.
Questioner: Was Miles a...
Brandon Sanderson: Yeah. Miles would be the same sort of thing.
Questioner: Is that why he didn't die as quickly in the execution?
Brandon Sanderson: Yes.
As to the mechanism of Feruchemical savantry, I would suggest that either there is healing "left over" that the Feruchemist somehow stores within their altered body, or that prolonged use alters their body's natural vitality.
It is possible, though he wasn't burning gold for its Allomantic effect (seeing your past selves) but for its Feruchemic effect (Feruchemic health). He was Compounding, burning the Feruchemic health he had storing in his metalminds.
He may have been the equivalent as a Feruchemist, or a compounding twinborn, as he was nearly constantly storing health in his 'minds, but I doubt he could be classed as a gold savant.