Will you have in Turbotax 2017, a section where one could use 2017 tax data to apply to the new 2018 tables to project 2018 taxes, if next year's income same?

Yes, using TurboTax for Desktop, you can produce a "What-If Worksheet" using 2018 tax tables.

1. Open your return and click on Forms in the upper right of the screen.  
2. Click on Open Form in the upper left of the screen.  
3. Type in what-if and click on Open to bring the form into the large window.  
4. With the What-If worksheet open you can check the box(es) under Description of Alternatives to use the 2018 tax rates for each scenario you will be running.

To return to the main section of TurboTax, click Step-by-Step in the header.

Why isn't this "what-if" feature built into the online version also? Seems like an obvious thing to offer customers since (I believe) most do not buy the desktop version.

HR Block has it!  C'mon turbo tax.  We need this on the online version!

I agree. I’ve been a customer of the online system for 5 years. Having the online version lack the ability  to use 2017 data and project taxes under the 2018 law is enough to have me change systems to another vendor.

Any idea if 2018 estimation is available in online version?

Online does not have the "what-if?" feature.  You can try the tax caster tool:
<a rel="nofollow" target="_blank" href="https://turbotax.intuit.com/tax-tools/calculators/taxcaster/">https://turbotax.intuit.com/tax-tools/calculators/taxcaster/</a>

@japappas3690  Online version is for simple tax returns, and so is TaxCaster, I suppose.
No need to switch vendors, switch to CD/Download.

Unbelievable that Intuit only provides the "what-if" estimating tool in the CD version!!!  How hard can it be to include the same programing into the online version?  REALLY?