The accordion being proposed here would be symmetrical with respect to the LH and RH button layouts. This is not a novelty by itself, but a particular accordion like this would still have certain characteristics of its own. For example, the low and high voice in the bass would be two octaves apart. Furthermore, on each side, the note C would be moved to the second row. On both sides, each C on the second row, and each F on the fourth row, would have a cross-hatched texture for tactile purposes.
The free bass would have five rows, but is that really necessary? Although it is possible to manage with only three rows, any additional duplicate row will allow for more comfortable fingering in some situations. For smooth legato fingering this can be especially useful. The fifth row can also make it easier to reach some of the tenth intervals (octave + third).
Why not make the bass buttons the same size as the buttons on the RH side? While this is possible if the intention is to use the thumb for a greater span of notes, it also means that the span becomes smaller than before when you don't use the thumb. This is because bigger buttons have to be spaced further apart. Since using the thumb on any other rows than the very first one seems somewhat uncomfortable, the ordinary smaller buttons would be recommended.
The proposed accordion would be a perfect companion to Nydana's alternative notation, called Modulo notation. To make full use of a free bass accordion like this, good sheet music arrangements can be a great help.
The following PDFs show the button layouts for the accordion that would have only chromatic layouts in both hands. The bass could be built as a simplified version of an existing converter accordion model. The reeds of the higher voice in the bass should be adapted for best performance when used together with the lower reeds: that is, apart from being two octaves above the lower reeds, their primary task should be to enhance the lower reeds. For this reason they should be rather soft and mellow.
The same PDF, but with Italian note names:
The SaLaTa version of nydanaacc.pdf:
SaLaTa and Modulo Notation are provided by Nydana