The date, I would imagine, wasn't chosen because it was a reasonable technical projection, but because 1999 is a high-value “pending-odometer-turnover” year.
Actually, I suspect that everything in that show was possible in 1999 (the base, the equipment, etc). But no-one wanted to pay the gazillion dollars it would have required.
Perhaps not the "stun gun".
It would be interesting to know if a properly-qualified engineer has ever taken a look at the Eagle and determined if it would be possible (e.g. with nuclear thermal rockets).