(PhD in music history, so I will just pontificate in as officious a manner as possible)
(also, former harpsichord student - I've always maintained that piano is a percussion instrument, so the notion of a 'drum guitar' is seriously LOL. But if you drum a guitar you get, I dunno, a flamenco guitar with touch plates?)
The piano was one of a huge number of 17th- and 18th-century experimental keyboard instruments. In pre-industrial times, it was easy to make keyboard instruments with all sort of weird designs. Most of these vanished; a couple had brilliant futures.
The best-known keyboard instruments were: the organ, which continued on through with various designs but no interruptions, the harpsichord (which plucked metal strings), which gradually dwindled out during the 18th century, and the fretted clavichord, which was by far the most common instrument, at least in Germany and Iberia. This worked by touching the strings with little brass blades. "Fretted" means that each set of strings could play more than one note, for example C and C-sharp would be played on the same set of strings by shortening the string, sort of like a guitar (they did this by angling the key-levers).
In addition to these 3 standard instruments, there were all sorts of experiments including the unfretted clavichord (each key played only one set of strings), the piano, the tangentenflügel (the strings were hit by jumpy little "jacks"), the lautenwerk (a harpsichord with gut strings, which must have been a monster to keep in tune), the geigenwerk (which produced a continuous sound by means of cranked rosin wheels; you can find modern replicas on youtube and they sound weirdly awful), the cembal d'amour (a kind of double-length clavichord), etc., etc.
The piano, in fact, was invented maybe independently several times, the first in Italy in the early 18th century, where it kind of died out, and then again in Germany a few decades later, with a different design. It took a little while to get enough kinks worked out before it started to catch on (JS Bach helped a bit here, actually, advising one of the makers about the tone).
So, the piano is just a survivor from the experimental period, and there's no historical connection with the guitar.
But I like the idea, anyway.