Some of the replies posted here about Instant TV Channel are not exactly correct. Most of the OP's requirements are available when using Instant TV Channel:
Video splash loading screen - Yes, this is available in Instant TV Channel.
Featured video on the top half of screen (title + short description on left, picture or clip on right) - Yes, this is available in Instant TV Channel using a grid (one or more selectable rows of posters) with custom row/poster sizes. You can even have trailer videos playing in a configurable area of the grid, similar to what you might see on Netflix.
Content headings on bottom half of screen (thriller, comedy, etc.) with horizontal scroll of videos - Depending on what you mean, this might be available with an Instant TV Channel grid.
Search function and content headings on farthest left part of screen listed vertically - Not available on the left side of the screen, but a customized grid might be similar. The in-channel search function can be accessed several different ways.
Multiple Vimeo showcases can be used in Instant TV Channel at the same time, for both Direct Publisher and SDK channels. A typical use in an SDK channel is one Vimeo showcase per row of a grid. AaronMSpelling is correct that Vimeo can get very expensive if your channel picks up a large number of viewers, but Vimeo is still a good place to start out. A Pro account, the minimum required for use with Roku, is currently $250 per year = $21 per month. They usually don't start hassling you to upgrade to a more expensive account until you hit a terabyte or two per month. You can always migrate off of Vimeo and onto a less expensive CDN at a later date.
Instant TV Channel does support in-channel purchases and subscriptions for SDK channels. It's not pricey at all and no outsourcing is required.
Documentation for most of this is available here: http://www.InstantTvChannel.com/help
