[teddyh]

Certainly, but the definition of “good” changes over time. At one point, callbacks were good, and now they’re not. What happens when the definition of “good” changes a second time before the code base has been fully converted from callbacks? Well, you shouldn’t write bad code, so now the code has three code styles in it, and, more importantly, two styles of conversions: From callbacks to current-good style and from previous-good style to current good style. This is harder to keep in your head, so conversion now goes more slowly.

[tcgv]

I share the same perspective. The value of a code base following one single coding style/convention/architecture is huge, even if there's a better coding approach right around the corner.