The 'Ŋ' and 'ŋ' characters are new. /ŋ/ is the lower-case equivalent of /Ŋ/.
In the current alphabet, digraphs ('ng' or 'nk') are used to represent a unique consonant that doesn't match either /n/ or /g/ (aka "hard g"). The rear of the tongue lifts up against the soft palette and seals airflow out the mouth, forcing it to exit the nose. We use this unique consonant whenever we pronounce the 'ing' in words like 'singing'. Compare 'linger' vs 'singer' vs 'sinner. In 'linger' the hard G is pronounced but in 'singer', it is not. If you take away the hard G, you're left with 'siner' (pronounce as 'sinner'). This does not match the sound of 'singer' because the /n/ sound is not the sound we make when saying 'singer'. It is a unique and separate consonant sound made using a different part of the tongue, sealing against a different part of the mouth. 7M-English therefore provides an exclusive character to represent this unique sound.