In the same vein as my suggested "Equipment" row, an "Initiative" row (probably placed just before or after the "Speed" row) would be a useful feature.
It would be handy to have an optional row in the stat block for monsters who have unusual bonuses to initiative, such as from special equipment. There are variant rules in the 5E DMG that involve calculating special initiative modifiers for players and monsters based on size, weapon type, etc. This is the kind of information that would be handy to have in a stat block.
Additionally, I like to create stat blocks to represent my players' combat capabilities because it's useful reference information, and players can sometimes have bonuses to initiative as well.
As such, an optional "Initiative" row would be useful.
I'd suggest implementing it as follows: an Initiative bonus "box" that is set to +0 by default. If the Initiative modifier for the monster is unchanged (equal to its DEX modifier) it is not listed. If the monster has an unusual bonus or penalty to initiative, this box's value can be modified, and the row appears in the stat block.
Additionally, a "custom initiative" checkbox wouldn't go amiss either. This would show the Initiative row even if it is unchanged, i.e. equal to the DEX modifier, and allow for custom notes to be added
e.g. "Initiative +2 (+5 in darkness or dim light)" kind of deal.