The biggest detriment on building wealth is paying taxes. That's why it's so important to take advantage of every allowable strategy to defer or lower tax liability. It's not about cheating the IRS, it's about using the rules to your advantage. Most people don't and end up significantly overpaying taxes.
As far as I know there hasn't been any established guidance yet on if personal property within real estate is allowable or not for a 1031. If it's still allowable then nothing has changed. Under the previous rules (which may still apply, we don't know yet) you needed to have equal or more 1250 property AND 1245 property to avoid any boot. If exchanging the 1245 property ends up being no longer allowable there will likely be an increase in partial dispositions and retirement of 1245 property or valuations showing that the 1245 property has little to no value. While these are already great strategies to significantly lower or eliminate recapture on 1245 property they would become almost necessary in a 1031 where they previously weren't.
Since the main point of the new tax law was to lower taxes on business and investment I think once it all washes out there isn't going to be any change regarding 1031's and cost segregation, remember most members of congress own property and they want the tax benefits of real estate as much as we do.
Unless your hold period is short and/or you jump several tax brackets between original purchase and eventual sale (1031 or otherwise) time value of money always wins! If either of those is the case you shouldn't be considering cost segregation in the first place; wait until you jump brackets then do a look back study to get the adjustment. I've had to tell several potential clients to wait until it makes sense.
Getting a $100,000 deduction in 2018 dollars and then repaying the same $100,000 deduction in 2038 dollars is a no-brainer. Those dollars will be worth much less in 2038. It's simple inflation. Other than those two situations above it makes way more sense to take that $100,000 deduction and reinvest it now rather than taking it over 39 or 27.5 years, each year that deduction is worth a little less even though it's the same dollar value. In the long term time value will always beat inflation. Plus look at the opportunity cost of reinvesting vs paying taxes.
It takes some creative structuring beyond my expertise, but I know there's at least 2 ways to significantly lower or virtually eliminate capital gains and recapture with or without a 1031. Some of it makes me go wow how is that legal, but it's black and white in the tax code and passes audit. With that it does take a very savvy tax attorney to get that stuff setup properly.
But as always, talk to a real estate tax attorney and a real estate CPA as well as a qualified cost segregation firm like mine or @Yonah Weiss. And make sure everyone understands everything, It's very common to hear "don't do that" when it's misunderstood.