The current system is a disaster. It seems every which way you turn you're getting taxed and taxed and taxed again. Then comes the disaster that is the Unaffordable Care Act that simply piles on more taxes, striking people with low incomes and poor health particularly hard. From what I can see if you can't make at least $30-40,000 from working you're probably better off not bothering. That doesn't seem like a good way to get people into the workforce.
Shifting taxation away from income and onto consumption makes a lot of sense, although I have many concerns about doing that.
My primary concern is that government is unlikely to leave income and payroll taxes at zero if they get a federal sales tax/VAT. The last thing we want is a federal sales tax only to find that in a few years time the government ran out of money (again) and figured they could change the rate of income tax from 0% to 2% and then slowly work it back up to a top rate of 30% or more.
A sales tax would need to be structured so that it didn't hammer the people at the bottom of the economic heap. The last thing the nation needs, especially for those earning around the standard deduction, is for the cost of absolutely everything to go up by 20% or more. (For comparison, the national rate of VAT in the UK is 20% for most products; across the EU I believe it ranges from about 18% to about 25%)
In the UK some products are subject to VAT and some are not. Food products are not subject to it, unless they are considered "luxury", which leaves all sorts of quirks in the system. You can buy biscuits without VAT but a thin layer of chocolate on them turns them into a luxury biscuit which is subject to 20% VAT. Clothing for children is not subject to VAT but clothing for adults is, but it's based on size so if you're an unusually large child your clothing costs went up 20% while if you're an unusually small adult you can dress for less. On the topic of "luxury food" a dispute some years ago over whether a particular food product was a cake or a biscuit went all the way to the High Court and racked up millions in assorted costs.
Because VAT is quite high it can often be cheaper to buy things abroad and bring them in to the country. You're supposed to declare them at Customs but you'd be amazed how forgetful people get when returning from a trip abroad. With France barely an hour away on the train it's easy to go abroad and bring things back. In that regard it's much like people who live near a state with zero sales tax can cross the state line, go shopping without the taxes and save some money. Maybe you're supposed to declare that and pay the taxes but crossing state and international lines seems to make people forgetful.
It's hard to avoid paying VAT when going shopping but if you're having work done by a tradesman you can often save a lot of money by paying in cash. As with tourists, you'd be amazed how a plumber or electrician can forget to charge the VAT because they were busy counting the cash you just gave them.
Registering for VAT as a business creates a headache because it's another return that has to be filed. You don't have to register in the UK until your turnover hits a particular level, which distorts the market because as soon as your turnover hits an arbitrary number you have to register and charge VAT, so all your prices jump.
If you are a VAT-registered entity then everything you buy is not subject to VAT (you may pay it but can reclaim it when you file your return). If you buy it to resell it or for internal use you don't pay the VAT. It's a huge incentive to branch out in your business - if you're a self-employed electrician with a passion for an expensive hobby and can find even the weakest justification to consider that hobby a business activity then all your gear just got cheaper.
Ultimately the end consumer will pay the taxes, just like always. The rich will find ways to avoid it and those who lack the means or the mentality to avoid paying will get hammered every which way, just like always. It would make a lot more sense for the government to stop spending money like a drunken sailor on shore leave and do what everybody else has to do - live within their means.
