Booking Holdings

TripAdvisor/FlipKey's challenges with the vacation rental industry aren't only technical ones. They also reflect increased supply available from individual homeowners and apartment renters. TripAdvisor, Booking.com and Airbnb are going after this sector and professionally managed properties are feeling the lumps.

As competitors close in and some do heavy TV advertising, HotelTonight states that it is doing "hundreds of millions of dollars" annually in gross bookings and that it has grown 100 percent per year over the last two years. This will continue to be an interesting skirmish between a well-funded startup focusing on last-minute versus larger players that can offer more wide-ranging solutions for hotels.

The challenge for TripAdvisor is whether it will win by being an all-encompassing app or whether it is better to be more focused like Expedia's or HotelTonight's apps. In phasing out its City Guides app, TripAdvisor is putting itself in the comprehensive camp.

Convergence is happening big time these days as online travel companies around the world, driven by the varied and changing accommodations' needs of their customers, are rapidly expanding and will continue to broaden their array of lodging options.

TripAdvisor, with its hotel and restaurant reviews, hotel bookings and tours and activities, is a much more well-rounded travel site than the younger Airbnb at this stage. Still, TripAdvisor has some Airbnb envy, and wants to take advantage of the sea changes in the global lodging industry.

Officials at Booking.com and Expedia know their hotel businesses are so far ahead of Amazon's nascent moves that they aren't cowering in fear at the might of Amazon. But you can bet they will be taking a hard look at the expanded Amazon Destinations today, as will the folks at Google and TripAdvisor.

The emergence of TripAdvisor as a viable booking site is a wake-up call to Expedia and the Priceline Group, who have been TripAdvisor's largest advertisers in recent years. It wouldn't be surprising to see them cut the spending spigot a bit.

Is Kayak abandoning metasearch? Not likely at all. But why not test photos and merchandising messaging on a site that is a Kayak offshoot instead of a Booking.com clone?

In contrast to its recent penchant for big acquisitions, the Priceline Group now seems to be content to take minority stakes, such as this one with Hotel Urbano, while Priceline focuses on integrating past acquisitions and its new B2B businesses.

Slack is becoming the messaging app of choice for modern work teams, and these nascent travel services are just the start. Expect more established business travel related services and new Slack-native services to crop up in coming months.