for my personal experience (as amateur developer)
imho... it's too early for beta.
remember what is it the beta: testing the real game (the whole game, not only separate sections) preparing for the final official release
consider what we have until now and consider what it must be yet done.
actually we have :
as cockpits: sidewinder, cobra (and probably soon, eagle)
as space station : the corolis st. (even with some glitches to be fixed).
as fuctions: just some basic spaceships settings and some basic spaceship functions, cockpit hud full functional except for cargo manteinance and hyperspace/supercruise travel.
combat multiplayers: in advanced state to be fixed furthermore.
seems a lot of things, but in facts they are few things.
to have a beta we should have at least:
as cockpits: the plan is to have 25 ships ? then we could start the beta with the 2/3 cockpits actually available with further update asap.
as space station: at least another kind over the corolis one + further updates (as the ships/cockpits).
as fuctions: we need the whole functions to play a beta - maps/cargo/selltradeinfos
as travel: i think we need the galaxy to start the beta, not only few stars systems ..and this is the major step for the whole game - once they are ready to drop the whole random generated galaxy we can begin to test the real game... not before that.
until that time it will be always an alpha stage and nothing more.
further things, further details of the game can be added in the beta stage (as Braben said in one of the devdiary)
so, i think you should be ready to consider other little alpha stages for the next months.
end of april/beginning of may: alpha 4: travel/trading with some star systems
whole may: fixing the bugs for alpha 4.
june/july: further alpha to fix or to add something more.
then the final alpha to test the whole galaxy when they are ready to update it in game. ----> beta