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>
Well, as @user2340231 mentioned this is an issue that has yet not been solved.
Nevertheless I found that installing the old OOoLatex extension that was available for OpenOffice, does the job.

In principle just follow the instructions on this ArchLinux wiki:
<https://wiki.archlinux.org/index.php/Ooolatex>

Download the extension from here:
<http://sourceforge.net/projects/ooolatex/files/OOoLatex/OOoLatex-4.0.0-beta/>
And also the fonts linked there: OOoLatexFonts.zip.

Install the extension by downloading it to your disk and opening the Extension Manager in Libre Office -> Tools.

Then also install the fonts, as mentioned in the wiki, in order to have available simple mathematical expressions in line with the text using the Expand option of the OOoLatex extension.

Restart LibreOffice and you are ready to go.

This worked for me on a manjaro Linux, but these steps are completely distribution-independent.