It reminds me when a company I worked for acquired a growing PHP-based platform with an active …

In this case it is not rewriting for the sake of rewriting, it’s moving content from one CMS to another which happens to be their main product. There is no reason to think this would not work out. The only code being rewritten is front end theme code, and some Wordpress plugins to support any unique tumblr features.

> I would be unsurprised if Automattic is using technical migration as busy-work. I would even suggest that, given this post's marketing and history[1], Automattic has realized they cannot grow Tumblr. I would also say that migration to WordPress is explicitly a marketing strategy for word press, their main product. Migrating a product you bought to be part of your main product is a pretty common corporate move.

> "You won’t even notice a difference from the outside." I can't recall the last time a company told the world about an internal migration, with no user impact, before the migration even started. Because likely it is not an internal migration with no user impact. Guess which part isn’t true, if they’re telling us.

Everything is guaranteed to be perfect when there is no deadline, or even timeframe estimate. Assurances without timelines are meaningless. It's more surprising they said much of anything at all this early in the process.