WordPress Calypso was released today and I must say it is an impressive effort from Automattic. Open Sourcing the contemporary interface will also drive forward not just the WordPress community, but the web in general.
Replacing the LAMP backend in due time is now a feasible in the future. Making the question whether the technical debt of WordPress matters moot.
With WordPress taking React, Flux and WebPack into use it also gives clarity that this front end development methodology will be rather future proof – even if Facebook would let go of React for one reason or another.