a guest should be able to use teams without needing an account
make it possible to easily establish "trust" relationships between Azure AD and Windows AD, so it will be possible to pick users from the "trusted" Windows AD and make them guests. Could be a light version of the normal trust, just enough so customers can get easy access. After the "trust" is established and a remote user is added, that user should get a mail (message) with a link. Clicking that link should bring the user straight into the online version of teams, at the right place and the right view. No questions, no prompts or anything else should be obstructing this process for the customer.
The same as point one for other Azure ADs
The customer might very well be the one providing the project manager, so it has to be possible to for guest users to have full access to the teams they are part of.
Guest needs access not only to teams, but also all other relevant and connected resources, such as sharepoint, OneDrive, VisualStudio.com and so on.
Each guest should have an InOrg contact person, which should be specified when inviting a guest. This contact person within the organization should be given permissions to manage this guest. But this management need to be available through the normal client tools. The contact person should get notified the first time the guest access teams. The guest should have a special consistent link/way to contact the contact person. It should appear in the same way and in the same place in all applications.
A guest who has a Office 365 subscription and perhaps already have the teams Client installed, should OBVIOUSLY be able to access everything from that (and other installed clients) AUTOMATICALLY! As soon has the guest is invited, it should CLEARLY show in the Teams application, and the guest should, without any fuss, just have access to the remote Team right there in the client. No switching to anything, no accounts, passwords or anything should be even visible to the guest unless he go looking for that kind of info. It should be just as if he joined a local team in his organisation. K.I.S.S!
It should be possible to grant team owners permission to invite guests to their team, DIRECTLY from the team client application.
Some customers don't use windows, so they might have g-mail accounts, apple accounts or something like that. It should be possible to invite individual guest based just on their email address. They would use this email address together with their normal password to login to their guest access to teams. Microsoft need to by default and automatically support and work seamlessly with all major login-providers (gmail, apple, linkedin, facebook, mail.ru, yandex and so on). These customers should NOT need to create a new account for an invitation to work.
And obviously, this has to work from any Office365 application. Sometimes you might initiate it from Sharepoint, or a user might initiate it by sharing files from his OneDrive, which could be a personal OneDrive, which normal users don't separate from their business onedrive (since it's all call OneDrive)