I've come across occasionally mentions of savoury meringues with flavours such as beetroot. How are these made? What is used as a substitute for the sugar? 
Well, you could always take a bite out of Adria's apple and just make foams directly from whatever liquid you wish to use (which may or may not be egg white; I'd advise against it. Why dilute your flavour?). Then add methylcellulose to provide you with the matrix you need for stability, and a standard ISI whipped cream dispenser will foam your product.  So for example, you could make a beetroot juice (250g) boiled with 50g sugar and 50g water, then cooled. Add methylcellulose 8g (2.2% by weight, using Methocel F50). Blend well. The recipe I have (for a carrot foam) calls for it to then be whipped in a stand mixer to stiff peaks, spread on a sheet and dehydrated for 5 hours. I imagine you could extrude from a standard ISI instead, probably charged twice with NO2.  Oh, as an added bonus, this would allow you to make completely vegan 'meringue' as well. Use a different liquid, add a touch of vanilla. 