It could, but the 951 heater is much faster, uses a different set of tips, is self calibrating and that's the true value of it, pretty much any iron that can senses the true tip temp without offset doesn't require calibration, implementing such is worth spending since it requires much more technology. The 937 uses the same technology as 888, except for its digital panel.
When makers recommend calibration, tip temp drifts away from cal for many reasons, and it can happen fairly quickly [ the 888 or 936 manual recommend calibration every time a tip, iron or heater is changed, not including wear of the current tip, so tip swapping routinely on 888 technology would really make the readout accuracy suffer if it were down to 1C as a LSD]. The basic technology of Metcal and clones and JBC are also self-calibrating. So what you see on the digital panel is truly what you get in self cal systems, always. So the 888 truly would not be on par with the 951 even if it has some of its features.
Now the question how much is self calibration worth, or fast temp ramp ups? I think if a user soldered much or is in a professional setting such as full time hand assemblers, you'd quickly see the value in fast heaters, self cal and hot swaps and move up to better stations. 888 is Hakkos' entry level station and for many folks who only solder for prototyping, low volume repair or hacking, its more than adequate. The FX951 is a next level up, but those curve performances aren't on par still with JBC or Metcal, which also cost more money; so there is a niche for every level of user.
If one wanted to improve the 888, what I think some useful add ons would be:
power on light
a method to hot swap tips
lower prices, especially the EU and UK market
I suspect it would cut into sales of the FX-951 if they had, so they intentionally restricted the feature set to prevent this.