According to today's CVS tree the problem with bootfloppy size has been 
resolved:

--- cut ---
#    create  bootfloppy/boot (from: /usr/build/dest/usr/mdec/boot)
#    create  bootfloppy/netbsd (from: 
/usr/build/obj/distrib/i386/instkernel/netbsd-INSTALL.gz)
gunzip -c /usr/build/obj/distrib/i386/instkernel/netbsd-INSTALL.gz > 
netbsd.tmp
/usr/build/tools/bin/i386--netbsdelf-strip -R .comment -R .ident netbsd.tmp
gzip -9c netbsd.tmp > netbsd; rm -f netbsd.tmp
#    create  bootfloppy/boot1.fs (from: boot  netbsd)
PAX=/usr/build/tools/bin/nbpax /bin/sh 
/usr/src/distrib/common/buildfloppies.sh  -i "/usr/build/tool
s/bin/nbinstallboot  -mi386 @IMAGE@ 
/usr/build/dest/usr/mdec/bootxx_ustarfs" -p  -m 3 -s .fs  boot 2
880 boot  netbsd
Running instboot: /usr/build/tools/bin/nbinstallboot -mi386 
floppy.5718.tar /usr/build/dest/usr/mdec
/bootxx_ustarfs
Free space in last tar block: boot 236, netbsd 147,
Writing 4423680 bytes (4320 KB) on 3 disks, padded by 1457152 bytes 
(1423 KB)
Creating disk 1 to boot1.fs
Creating disk 2 to boot2.fs
Creating disk 3 to boot3.fs
0+1 records in
1+0 records out
1474560 bytes transferred in 0.026 secs (56713846 bytes/sec)
Final result:
-rw-r--r--  1 root  wheel  1474560 Nov 18 02:07 boot1.fs
-rw-r--r--  1 root  wheel  1474560 Nov 18 02:07 boot2.fs
-rw-r--r--  1 root  wheel  1474560 Nov 18 02:07 boot3.fs
--- cut ---

Though looks like there's the same problems with bootfloppy-big:

--- cut ---
#    create  bootfloppy-big/boot (from: /usr/build/dest/usr/mdec/boot)
#    create  bootfloppy-big/USTAR.volsize.13200
#    create  bootfloppy-big/netbsd (from: 
/usr/build/obj/distrib/i386/instkernel/netbsd-INSTALL.gz)
gunzip -c /usr/build/obj/distrib/i386/instkernel/netbsd-INSTALL.gz > 
netbsd.tmp
/usr/build/tools/bin/i386--netbsdelf-strip -R .comment -R .ident netbsd.tmp
gzip -9c netbsd.tmp > netbsd; rm -f netbsd.tmp
#    create  bootfloppy-big/boot-big1.fs (from: boot USTAR.volsize.13200 
netbsd)
PAX=/usr/build/tools/bin/nbpax /bin/sh 
/usr/src/distrib/common/buildfloppies.sh  -i "/usr/build/tool
s/bin/nbinstallboot  -mi386 @IMAGE@ 
/usr/build/dest/usr/mdec/bootxx_ustarfs" -p  -m 1 -s .fs  boot-b
ig 5760 boot USTAR.volsize.13200 netbsd
Running instboot: /usr/build/tools/bin/nbinstallboot -mi386 
floppy.5846.tar /usr/build/dest/usr/mdec
/bootxx_ustarfs
Free space in last tar block: boot 236, netbsd 147,
buildfloppies.sh: Image is 1683 bytes (1 KB) too big to fit on 1 disk

*** Failed target:  boot-big1.fs
*** Failed command: PAX=/usr/build/tools/bin/nbpax /bin/sh 
/usr/src/distrib/common/buildfloppies.sh
-i "/usr/build/tools/bin/nbinstallboot -mi386 @IMAGE@ 
/usr/build/dest/usr/mdec/bootxx_ustarfs" -p -m
  1 -s .fs boot-big 5760 boot USTAR.volsize.13200 netbsd
*** Error code 1

Stop.
nbmake: stopped in /usr/src/distrib/i386/floppies/bootfloppy-big
--- cut ---

// wbr