There are smaller negative pressure ventilator options like the Cuirass from Hayak medical. This is essentially a barrel-like chamber you wear over your abdomen which creates a vacuum allowing ventilation support. You breathe into a 'negative space' and thus gain support. It has advantages and drawbacks.

I have used this with two patients with Motor Neuron Disease both of which could not cope with positive pressure ventilation via a face mask (NIV) and it worked well, that is to say they had symptomatic relief.

This treatment was done at the patient's home overnight and during the day as their disease progressed. The Cuirass shell itself is cumbersome and the ventilator is large and noisy so this isn't a great option (but the only one we had considering the decision not to have a trach). The only reason it was successful is because both these patients and their families were highly committed and willing to put up with the difficulties of using the device. It's certainly not for everyone.

I asked myself the same question about whether this technology was developing and would improve but I think that as the majority of patients cope with NIV there is no impetus to throw money at negative pressure. Indeed negative pressure ventilation via Cuirass is a less recent development than NIV and I think it's unlikely to improve because NIV is so 'easy'.

Speaking as a specialist nurse in home ventilation so happy to be corrected/expanded upon

Edit: with respect to ventilating neuromuscular patients it very much depends on the condition. I have many patients with Duchene's Muscular Dystrophy who have been on NIV for well over a decade and are coping really well. These patients seem to me more likely to die from their cardiac issues than respiratory when managed well on a ventilator.