You definitely do not want to start a project before you know the idea is feasible, but let me ask this: in strict terms, couldn't the feasibility practices be a project themselves?  Wouldn't you want to manage feasibility like a project if it was sufficiently large enough to warrant doing so?

How would this apply to a medical device idea?

Feasibility studies are important and assess whether or not the project can realistically be done. In other words, it tests whether the protocol and the planned procedures work together properly to inform the stakeholders whether or not it is worth carrying out in full. With regards to a medical device, there are various aspects that need to be considered before carrying them out including site selection and the training of participants. For the site, the location can heavily influence the quantity,  types, and duration of participants that would be entering the study which are all crucial factors for the study. For training, all participants would need to be educated on the purpose of a novel device and the potential to improve clinical care, patient outcomes, and advance the standard of care.

Feasibility study is very important for the success of any project as it help in developing different methods to help you deal with your project with modern and advanced methods and studying the market, which helps you to understand the volume of demand for things extracted from your project
Doing a successful feasibility study for a project can be done by collecting economic data, Careful and detailed analysis of the target market, measuring the ratio of supply and demand, and the competitions that exist among other projects, and determine all the stages of your project growth, as your project begins with a small size in an experimental way, then moves from the stages stage to stage of its growth until it grows in size, and the matter also happens with the profits that you expect to achieve after the success of all stages of your project growth

A feasibility study is essentially a process for determining the viability of a
proposed initiative or service and providing a framework and direction for
its development and delivery

This also gives project teams more focus and provides an alternative outline
Identifies a valid reason to undertake the project

I agree that the feasibility practices themselves could be projects. For example, in the medical device industry, a goal may not be to create a new medical device, but to see the feasibility of an existing medical device in treating something it is not typically used for. With the idea/goal being the feasibility of the device in treating a new case and not necessarily the creation of a new device, the feasibility can be treated as a project. In this case, you would want to treat the feasibility as a project, as it requires a large amount of organization and planning that is also present in a project. 

In terms of the viability of the project, I believe that the viability is not predictive of the success of the project, since many variables come into play for the success of the project. However, as previously mentioned, before initiation of the project, the viability or feasibility must be already determined. During the product life cycle, there may be changes in the features of the product and the feasibility of adding a feature or changing a specification needs to be tested. For this case, the feasibility practice is more a part of the project, rather than its own individual project. 

The site projectmanager.com recommends the following steps for a feasibility study:

1. Conduct a Preliminary Analysis
2. Prepare a Projected Income Statement
3. Conduct a Market Survey, or Perform Market Research
4. Plan Business Organization and Operations
5. Prepare an Opening Day Balance Sheet
6. Review and Analyze All Data
7. Make a Go/No-Go Decision

A Preliminary analysis in the context of medical devices might be prototyping, or animal testing.
Also identifying a unserved need, a market where the demand is greater than the supply, and whether the product or service has a distinct advantage. This part could take a long time and cost considerable finances in itself since the preliminary analysis would need to have a budget to conduct it associated activities.

I think testing feasibility is making sure that the product can be made, which is researching different solutions to the problem in order to find one or the best one. The other aspect of feasibility is money. How much do we have to spend on each part of the project (research, marketing, testing)? Also how much can you make from the product (market research)? With every project there's an element of monetary risk that a company has to take to make the product, I think part of feasibility is the initial assessment of whether the risk is worth it.