I don't think it's reasonable to say we're in a bubble because of a $80M fund around developing for a new platform. Few companies truly become platforms, and it's a misnomer to call it a bubble if this only happens to one company. It takes a lot of money or momentum to develop one. Facebook had by far the most compelling one in the last ten years, and the obvious incentive there was it's >300M users at the time. The case is less compelling for a B2B platform like Slack, but it makes sense as many of these investors also invest in B2B startups that can gain huge visibility through the Slack platform.

By having six investors in the fund, each fund can mitigate risk of Slack's platform not getting traction while lowering the barrier for developers to enter. This slideshow by A16Z outlines why the venture capitalists (including some on the list of Slack fund contributors) are tightening their belts around investing and telling companies like Slack to generate reliable business models rather than IPO prematurely.

This premature IPO behavior was the reason for the last bubble, and I think this investment fund is proof that we are NOT in a bubble. The new strategy for these investment funds is to allow their startups to generate revenue on a much more stable basis without the need to go public (and get cash for equity) for this to happen. Most B2B companies would eventually benefit from a recurring-fees model built around the Slack platform, and this enables smaller, fledging companies to scale much more quickly towards long-term cashflow positivity.

In all, the kings of tech companies are those that find some sort of platform or natural monopoly. Slack may be next in line to follow Airbnb, Uber, Twitter, Facebook, and Google respectively. Overall, by allowing a method to build these platforms while not going public, investors increase returns for their companies in the short AND LONG term while maintaining a course of innovation!