Is it possible to make such a Scope device : something wich take pc keyboard special buttons (like play/ stop or vol+ - vol-) and convert it into midi ?
any midi device has it by default but only with a few keys (page up/down home/end and all the keys that have functions to play with potis or buttons.
it converts in midi when a midi CC is assigned. (example: potis has midi CC, now when you move the potis with the keyboard, it sends midi).
Not what, i know, you want but that's all you can make inside scope for what i know. More than that requires native programs that are run at windows level, to transform an input devices (keyboard, joystick etc) into midi (or programming new dsp in a dsp coding app, if that's possible).
doing it inside scope is useful only if you want to send midi out of scope (to hardware or to record poti/fader movements in daws).
beleive me, what you want is to complicated considering what you want to achieve (press play with a key that actually has a "play" icon
... i know what you are going thru
but nothing seems to be simple in this world, lol...
Now, if you forget about midi (i don't understand what it is for exactly anyway)
what you can do, is take a programmable keyboard (logitech gamer kb or microsft digital media keyboard 3000 (*), where you can change the play/stop keys to send messages like "page up/down" etc. but it removes the function with other programs.
The other solutions is to have a programmable keyboard with empty keys or a button pad, and to program them to send shortcuts to a daw or to scope. I have a couple of those, that i used in daws and scope to make keyboard macros, but not to send midi or do anything midi (except with the Tetra CC editor where the page up/down are better than potis to program osc frequencies, bpm and a couple of other functions).
there is also a software that allows to assign various keys and macros to your pc keyboard (for example, i type / and it sends : Q ctrl+Q , or arrow down + enter etc etc, just like a macro keyboard. But i forgot the name, i desinstalled it long ago
(because you need to think to start the app etc, which is just boring - while good keyboard hardware can change profile automatically according to the app active on screen so you don't need to think about anything).
(*) I did reprogram mine to send space bar to control daws, with a nice looking button qith the "play/pause" icons on it, but it wasn't great, was fun 5 minutes, and now i am back to the classic shortcuts that i am used to. For all the other (actually useful) stuff, the logitech g13 is much better (probably the keyboards are also good but expensive and very large, like 60 cm large) and also the belkin n52te but much less responsive than the g13. I use the belckin on the midi keyboard, to control daw when i don't see the screen (15 functions to record midi tracks fast). it is good for the neck not to turn around each time
logitech rules in this area (precision, reactivity, macros etc).
you can have a button to make the macro "create new midi track + double-clic to create an event (*) + select pencil tool", and then all is automatic and you just need to draw a line on your screen for a note to trigger your dsp sequencers
(*) i don't use such macros, but mouse-click simulations are available only in belkin/razer gamepads if i remember well, not logitech.
Nocturn is as cheap as chips but is incredibly useful. 