I'm getting a bit further now, but would appreciate some more help.
I have a headless NeXT booting the netboot image from BOOTP/TFTP,
then the kernel from NFS.  I get the following output, then nothing:

Welcome to NetBSD/next68k
Constructing the segment list...
machine type = 0x01
board rev = 0x01
dmachip = 0x00000139
diskchip = 0x00000136
Looks like a NeXT_WARP9
Memory bank 0x00 has value 0x06
Memory bank 0x01 has value 0x05
Memory bank 0x02 has value 0x00
Memory bank 0x03 has value 0x00
Memory segments found:
        0x04000000 - 0x04400000
        0x05000000 - 0x05ffe000
Ethernet address: 00:00:0f:00:e2:3c
Check serial port A for console.

Incidentally, it appears that the messages prior to these do not send
CRLF, just LF.

A tcpdump just shows NFS getattr requests with replies of "ok":
10:40:44.359170 207.107.26.17.1159930030 > seka.netbsd.canuck.com.nfs: 96 getattr [|nfs] (ttl 64, id 181)
10:40:44.359316 seka.netbsd.canuck.com.nfs > 207.107.26.17.1159930030: reply ok 112 getattr [|nfs] (ttl 64, id 11316)
10:40:44.361326 207.107.26.17.1159930031 > seka.netbsd.canuck.com.nfs: 96 getattr [|nfs] (ttl 64, id 182)
10:40:44.361457 seka.netbsd.canuck.com.nfs > 207.107.26.17.1159930031: reply ok 112 getattr [|nfs] (ttl 64, id 11317)
10:40:44.363692 207.107.26.17.1159930032 > seka.netbsd.canuck.com.nfs: 96 getattr [|nfs] (ttl 64, id 183)
10:40:44.363824 seka.netbsd.canuck.com.nfs > 207.107.26.17.1159930032: reply ok 112 getattr [|nfs] (ttl 64, id 11318)
10:40:44.369920 207.107.26.17.1159930033 > seka.netbsd.canuck.com.nfs: 96 getattr [|nfs] (ttl 64, id 184)
10:40:44.370144 seka.netbsd.canuck.com.nfs > 207.107.26.17.1159930033: reply ok 112 getattr [|nfs] (ttl 64, id 11319)
10:40:44.372148 207.107.26.17.1159930034 > seka.netbsd.canuck.com.nfs: 96 getattr [|nfs] (ttl 64, id 185)
10:40:44.372284 seka.netbsd.canuck.com.nfs > 207.107.26.17.1159930034: reply ok 112 getattr [|nfs] (ttl 64, id 11320)

These repeat every so often (two minutes or so).

I'd appreciate any suggestions as to what might be going on.

Thanks,
-allen