Your post is well thought out. Especially your "geocities, angelfire, and a host of other failed buys in the graveyard." part.
Thank you. I'll assume there was a hint of sarcasm in your post and address it in another well thought out post.
Tumblr is very much a blog centric type platform, which a huge amount of x-rated/NSFW type content. Now that Yahoo is taking it as their own, they will need be advertising on it.
One of the reasons so many people use tumblr is the lack of advertising on it, and the ability to freely post all types of content.
When yahoo starts running ads on it, those advertisers are going to not advertise on a platform delivering so much NSFW content.
Yahoo is going to filter/separate/reduce the NSFW content on tumblr.
Tumblr users are going to go find another platform to post their content.
Users will leave tumblr.
Tumblr will become a ghost town
Wall Street will mock yahoo for purchasing tumblr and we will be talking about this day forever more when we discuss the top 10 worst corporate buys in the history of business.