The likelihood of the IRS resorting to collection of taxes through asset seizure — probably the most severe tax collection method — can only accurately be determined on a case-by-case basis*. Certainly the IRS has authority to seize and sell assets in order to satisfy a tax debt, but it has to make sense for the Service to do so. They want to be sure that the target asset (or assets) will raise enough money to cover all or most of what is owed. They want to be sure that the profits from the seizure and sale will at least match the effort and preparation going into the procedure.
Furthermore, the IRS has internal guidelines dictating when and how they may proceed with asset seizures. In other words, the IRS doesn’t normally go after granny’s little two bedroom farm house, but there are exceptions. The IRS doesn’t like to boot people out of their primary residence; it’s not good public policy and not a great PR move. And the IRS doesn’t normally resort to seizure at all if they can collect what is owed through other means. Much more common is the wage garnishment, bank levy, and federal tax lien. Of course the preferred method of tax collection is through voluntary payment, but not everybody pays their taxes so willingly.
But don’t be mistaken, the IRS can and will seize assets, primarily real property, vehicles, and valuable estate assets. Local news outlets often advertise IRS public auction dates. The IRS also posts details about asset sales on their dedicated auction website. If you do attend an IRS auction, you should know that they don’t accept personal checks, and they don’t take American Express.
*You might argue that the most severe IRS collection tool is criminal prosecution and prison sentences; however, I don’t know if I would consider this a collection method, except to the extent that it encourages others to file and pay on time.