Question: I want to create a presentation in Impress and need to embed a formula in text. I only found very old forum posts (over five years old), which said it is not possible.

Has this changed by now? How can I do it?

Answer: 
No, it is not possible to embed a formula or a graphical object in text in draw and impress.

In Libreoffice/Openoffice terms this would be called "anchoring the formula as a character". This is something that is possible in writer (contrary to one of the answers above).

TeXMaths is a great addition to Libreoffice, but can in no way help on this issue.

Unfortunately, this is a great deficiency that makes impress very very badly suited for any serious scientific presentation.

If you want to follow the state of this issue, look at <https://www.libreoffice.org/bugzilla/show_bug.cgi?id=35033>

If you want to support the addition of this feature to libreoffice, there is a bounty that you can contribute to at <http://www.freedomsponsors.org/core/issue/473/allow-inline-graphics-formulas-in-impress-and-draw>
You can follow a trick like this:
Select any text that you want, for ex: this is length h\_0 of flat plate....

then you select h\_0, then you go to Insert -> Object -> Formula  

you will get what you want, the formula in the line